diff --git a/backend/mci-server/src/main/java/com/sino/mci/channel/service/ChannelAccountService.java b/backend/mci-server/src/main/java/com/sino/mci/channel/service/ChannelAccountService.java
index a66c5b1..66276ed 100644
--- a/backend/mci-server/src/main/java/com/sino/mci/channel/service/ChannelAccountService.java
+++ b/backend/mci-server/src/main/java/com/sino/mci/channel/service/ChannelAccountService.java
@@ -234,6 +234,12 @@ public class ChannelAccountService {
             person = personMapper.selectById(identity.getPersonId());
             person.setPersonName(contact.getName());
             person.setPhone(contact.getMobile());
+            Person existing = personMapper.selectById(person.getId());
+            if (existing != null) {
+                person.setInstitutionId(existing.getInstitutionId());
+                person.setSupplierId(existing.getSupplierId());
+                person.setPersonType(existing.getPersonType());
+            }
             personMapper.updateById(person);
 
             identity.setChannelUserName(contact.getName());
@@ -273,6 +279,13 @@ public class ChannelAccountService {
             conversation.setConversationName(conv.getChatName());
             conversation.setOwnerAccountId(account.getId());
             conversation.setSubjectId(subjectId);
+            Conversation existing = conversationMapper.selectById(conversation.getId());
+            if (existing != null) {
+                conversation.setInstitutionId(existing.getInstitutionId());
+                conversation.setSupplierId(existing.getSupplierId());
+                conversation.setContractId(existing.getContractId());
+                conversation.setChannelCode(existing.getChannelCode());
+            }
             conversationMapper.updateById(conversation);
             return conversation;
         }
diff --git a/backend/mci-server/src/test/java/com/sino/mci/channel/controller/WeComSyncTest.java b/backend/mci-server/src/test/java/com/sino/mci/channel/controller/WeComSyncTest.java
index 0a29874..3846943 100644
--- a/backend/mci-server/src/test/java/com/sino/mci/channel/controller/WeComSyncTest.java
+++ b/backend/mci-server/src/test/java/com/sino/mci/channel/controller/WeComSyncTest.java
@@ -179,6 +179,84 @@ class WeComSyncTest {
         assertThat(receiveMaster).isNotNull();
     }
 
+    @Test
+    void shouldPreservePersonBusinessFieldsDuringContactSync() throws Exception {
+        String authToken = createTenantAndLogin(mockMvc, TENANT_CODE, "企微同步租户");
+        ChannelAccount account = createWeComAccount();
+
+        Person person = new Person();
+        person.setTenantCode(TENANT_CODE);
+        person.setPersonCode("user001");
+        person.setPersonName("原始姓名");
+        person.setPhone("13800138001");
+        person.setPersonType(1);
+        person.setInstitutionId(100L);
+        person.setSupplierId(200L);
+        person.setStatus(1);
+        personMapper.insert(person);
+
+        ChannelIdentity identity = new ChannelIdentity();
+        identity.setTenantCode(TENANT_CODE);
+        identity.setPersonId(person.getId());
+        identity.setChannelType(CHANNEL_TYPE);
+        identity.setChannelUserId("user001");
+        identity.setChannelUserName("原始姓名");
+        identity.setSubjectId(account.getSubjectId());
+        identity.setStatus(1);
+        channelIdentityMapper.insert(identity);
+
+        mockMvc.perform(post("/msg-platform/api/v1/channel-account/{account_id}/sync-contacts", account.getId())
+                        .contextPath("/msg-platform")
+                        .header("Authorization", authToken)
+                        .header("X-Tenant-Code", TENANT_CODE)
+                        .contentType(MediaType.APPLICATION_JSON))
+                .andExpect(status().isOk())
+                .andExpect(jsonPath("$.code").value(0));
+
+        Person updated = personMapper.selectById(person.getId());
+        assertThat(updated.getPersonName()).isEqualTo("张三");
+        assertThat(updated.getInstitutionId()).isEqualTo(100L);
+        assertThat(updated.getSupplierId()).isEqualTo(200L);
+        assertThat(updated.getPersonType()).isEqualTo(1);
+    }
+
+    @Test
+    void shouldPreserveConversationBusinessFieldsDuringConversationSync() throws Exception {
+        String authToken = createTenantAndLogin(mockMvc, TENANT_CODE, "企微同步租户");
+        ChannelAccount account = createWeComAccount();
+
+        Conversation conversation = new Conversation();
+        conversation.setTenantCode(TENANT_CODE);
+        conversation.setConversationType(2);
+        conversation.setChannelType(CHANNEL_TYPE);
+        conversation.setChannelConversationId("chat001");
+        conversation.setOwnerAccountId(account.getId());
+        conversation.setSubjectId(account.getSubjectId());
+        conversation.setConversationName("原始群名");
+        conversation.setInstitutionId(100L);
+        conversation.setSupplierId(200L);
+        conversation.setContractId(300L);
+        conversation.setChannelCode("ORIGINAL");
+        conversation.setCreateSource(1);
+        conversation.setStatus(1);
+        conversationMapper.insert(conversation);
+
+        mockMvc.perform(post("/msg-platform/api/v1/channel-account/{account_id}/sync-conversations", account.getId())
+                        .contextPath("/msg-platform")
+                        .header("Authorization", authToken)
+                        .header("X-Tenant-Code", TENANT_CODE)
+                        .contentType(MediaType.APPLICATION_JSON))
+                .andExpect(status().isOk())
+                .andExpect(jsonPath("$.code").value(0));
+
+        Conversation updated = conversationMapper.selectById(conversation.getId());
+        assertThat(updated.getConversationName()).isEqualTo("测试客户群");
+        assertThat(updated.getInstitutionId()).isEqualTo(100L);
+        assertThat(updated.getSupplierId()).isEqualTo(200L);
+        assertThat(updated.getContractId()).isEqualTo(300L);
+        assertThat(updated.getChannelCode()).isEqualTo("ORIGINAL");
+    }
+
     private ChannelAccount createWeComAccount() {
         ChannelSubject subject = new ChannelSubject();
         subject.setTenantCode(TENANT_CODE);
diff --git a/scripts/regression/wecom-sync-protect-business-fields.sh b/scripts/regression/wecom-sync-protect-business-fields.sh
new file mode 100644
index 0000000..308748b
--- /dev/null
+++ b/scripts/regression/wecom-sync-protect-business-fields.sh
@@ -0,0 +1,140 @@
+#!/bin/bash
+set -e
+
+# Regression script for Task 1: business fields must survive WeCom sync.
+#
+# Pre-requisites:
+#   - mci-server is running (default http://localhost/msg-platform)
+#   - WeCom sync client is mocked or the real client returns a conversation
+#     whose channelConversationId matches the one created below.
+#   - The conversation API currently does NOT expose contractId/institutionId/
+#     supplierId/channelCode, so after creating the conversation via API you
+#     must set contract_id = 100 directly in the DB (or extend the DTO).
+#   - jq and curl are installed.
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+cd "$SCRIPT_DIR/../.."
+
+BASE_URL="${BASE_URL:-http://localhost/msg-platform}"
+
+command -v curl >/dev/null 2>&1 || { echo "curl is required but not installed."; exit 1; }
+command -v jq >/dev/null 2>&1 || { echo "jq is required but not installed."; exit 1; }
+
+TENANT_CODE="wecom-boundary-$(date +%s)"
+
+make_request() {
+  local method=$1
+  local url=$2
+  local payload=$3
+  shift 3
+  local headers=("$@")
+
+  if [ "$method" = "GET" ]; then
+    curl -s -S -X GET "${headers[@]}" "$url"
+  elif [ -n "$payload" ]; then
+    curl -s -S -X "$method" "${headers[@]}" -H "Content-Type: application/json" -d "$payload" "$url"
+  else
+    curl -s -S -X "$method" "${headers[@]}" -H "Content-Type: application/json" "$url"
+  fi
+}
+
+assert_code_zero() {
+  local name=$1
+  local response=$2
+  local code
+  code=$(echo "$response" | jq -r '.code // .errcode // empty')
+
+  if [ "$code" = "0" ]; then
+    echo "[PASS] $name"
+    return 0
+  else
+    echo "[FAIL] $name (code=$code)"
+    echo "       response: $response"
+    exit 1
+  fi
+}
+
+# 1. Create tenant
+echo "==> 1. Create tenant"
+TENANT_RESPONSE=$(make_request POST "$BASE_URL/api/v1/account/tenant" \
+  "{\"tenantCode\":\"$TENANT_CODE\",\"tenantName\":\"WeCom Boundary Test\"}")
+assert_code_zero "Create tenant" "$TENANT_RESPONSE"
+
+# 2. Create admin user and login
+echo "==> 2. Create admin user and login"
+make_request POST "$BASE_URL/api/v1/account/user" \
+  '{"username":"admin","password":"admin123","realName":"Admin","roleCodes":["tenant_admin"]}' \
+  -H "X-Tenant-Code: $TENANT_CODE" >/dev/null
+
+LOGIN_RESPONSE=$(make_request POST "$BASE_URL/api/v1/account/login" \
+  '{"username":"admin","password":"admin123"}' \
+  -H "X-Tenant-Code: $TENANT_CODE")
+assert_code_zero "Login" "$LOGIN_RESPONSE"
+TOKEN=$(echo "$LOGIN_RESPONSE" | jq -r '.data.token')
+AUTH_HEADER="Authorization: Bearer $TOKEN"
+COMMON_HEADERS=(-H "$AUTH_HEADER" -H "X-Tenant-Code: $TENANT_CODE")
+
+# 3. Create channel subject (corp credentials are required for sync)
+echo "==> 3. Create channel subject"
+SUBJECT_RESPONSE=$(make_request POST "$BASE_URL/api/v1/channel-subject" \
+  '{"channelType":"wecom","subjectCode":"sino","subjectName":"Sino Boundary","corpId":"ww-boundary","corpSecret":"secret","agentId":"1000002"}' \
+  "${COMMON_HEADERS[@]}")
+assert_code_zero "Create channel subject" "$SUBJECT_RESPONSE"
+SUBJECT_ID=$(echo "$SUBJECT_RESPONSE" | jq -r '.data.id')
+
+# 4. Create channel account
+echo "==> 4. Create channel account"
+ACCOUNT_RESPONSE=$(make_request POST "$BASE_URL/api/v1/channel-account" \
+  "{\"accountType\":1,\"channelType\":\"wecom\",\"accountId\":\"boundary-account\",\"accountName\":\"Boundary Account\",\"subjectId\":$SUBJECT_ID}" \
+  "${COMMON_HEADERS[@]}")
+assert_code_zero "Create channel account" "$ACCOUNT_RESPONSE"
+ACCOUNT_ID=$(echo "$ACCOUNT_RESPONSE" | jq -r '.data.id')
+
+# 5. Create conversation via API
+echo "==> 5. Create conversation"
+CONVERSATION_RESPONSE=$(make_request POST "$BASE_URL/api/v1/conversation" \
+  '{"conversationType":2,"channelType":"wecom","channelConversationId":"chat-boundary-001","conversationName":"Boundary Group"}' \
+  "${COMMON_HEADERS[@]}")
+assert_code_zero "Create conversation" "$CONVERSATION_RESPONSE"
+CONVERSATION_ID=$(echo "$CONVERSATION_RESPONSE" | jq -r '.data.id')
+
+# 6. Set business fields in DB (contract_id=100).
+#    The public API does not expose these fields yet, so this step is performed
+#    directly in the database. Example:
+#
+#      UPDATE mci_conversation
+#      SET contract_id = 100,
+#          institution_id = 1000,
+#          supplier_id = 2000,
+#          channel_code = 'ORIGINAL'
+#      WHERE id = <CONVERSATION_ID>;
+#
+echo "==> 6. Set contractId=100 in DB for conversation $CONVERSATION_ID"
+echo "       (execute the SQL shown in the script comments, then press any key)"
+read -r -n 1 -s || true
+
+# 7. Call sync-conversations
+echo "==> 7. Call sync-conversations"
+SYNC_RESPONSE=$(make_request POST "$BASE_URL/api/v1/channel-account/$ACCOUNT_ID/sync-conversations" \
+  '' "${COMMON_HEADERS[@]}")
+assert_code_zero "Sync conversations" "$SYNC_RESPONSE"
+
+# 8. Query conversation and assert contractId is still 100
+echo "==> 8. Query conversation and assert business fields"
+QUERY_RESPONSE=$(make_request GET "$BASE_URL/api/v1/conversation/$CONVERSATION_ID" \
+  '' "${COMMON_HEADERS[@]}")
+assert_code_zero "Query conversation" "$QUERY_RESPONSE"
+
+CONTRACT_ID=$(echo "$QUERY_RESPONSE" | jq -r '.data.contractId // empty')
+if [ "$CONTRACT_ID" = "100" ]; then
+  echo "[PASS] contractId preserved (100) after sync"
+else
+  echo "[FAIL] contractId was overwritten or not set (got '$CONTRACT_ID')"
+  echo "       response: $QUERY_RESPONSE"
+  exit 1
+fi
+
+echo ""
+echo "========================="
+echo "All regression checks passed."
+echo "========================="