diff --git a/src/main/java/com/company/agentfoundation/integration/wecom/service/WecomStudentContactStatsService.java b/src/main/java/com/company/agentfoundation/integration/wecom/service/WecomStudentContactStatsService.java
index 9095f81..fa0b96e 100644
--- a/src/main/java/com/company/agentfoundation/integration/wecom/service/WecomStudentContactStatsService.java
+++ b/src/main/java/com/company/agentfoundation/integration/wecom/service/WecomStudentContactStatsService.java
@@ -25,6 +25,7 @@ public class WecomStudentContactStatsService {
   private static final Logger log = LoggerFactory.getLogger(WecomStudentContactStatsService.class);
   private static final ZoneId CHINA_ZONE = ZoneId.of("Asia/Shanghai");
   private static final int BATCH_SIZE = 100;
+  private static final int API_WINDOW_DAYS = 30;
 
   private final WecomClient wecomClient;
 
@@ -59,8 +60,8 @@ public class WecomStudentContactStatsService {
     int rangeNew = (int) earliestCreateTimeByStudent.values().stream()
         .filter(createTime -> createTime != null && createTime >= rangeStart && createTime < rangeEndExclusive)
         .count();
-    BehaviorSummary behaviorSummary = fetchBehaviorSummary(followUsers, rangeStart, rangeEndExclusive - 1);
-    GroupMessageSummary groupMessageSummary = fetchGroupMessageSummary(rangeStart, rangeEndExclusive - 1);
+    BehaviorSummary behaviorSummary = fetchBehaviorSummary(followUsers, startDate, endDate);
+    GroupMessageSummary groupMessageSummary = fetchGroupMessageSummary(startDate, endDate);
 
     return new WecomStudentContactStats(
         allStudents.size(),
@@ -107,7 +108,7 @@ public class WecomStudentContactStatsService {
     }
   }
 
-  private BehaviorSummary fetchBehaviorSummary(List<String> followUsers, long startTime, long endTime) {
+  private BehaviorSummary fetchBehaviorSummary(List<String> followUsers, LocalDate startDate, LocalDate endDate) {
     int newApplyCount = 0;
     int newContactCount = 0;
     int chatCount = 0;
@@ -118,33 +119,41 @@ public class WecomStudentContactStatsService {
     long avgReplyTimeWeightedSum = 0L;
     long avgReplyTimeWeight = 0L;
 
-    for (int start = 0; start < followUsers.size(); start += BATCH_SIZE) {
-      List<String> batchUsers = followUsers.subList(start, Math.min(start + BATCH_SIZE, followUsers.size()));
-      WecomUserBehaviorDataResponse response = wecomClient.getStudentContactBehaviorData(batchUsers, startTime, endTime);
-      List<WecomUserBehaviorDataResponse.BehaviorData> behaviorData = response.behaviorData();
-      if (behaviorData == null) {
-        continue;
-      }
-      for (WecomUserBehaviorDataResponse.BehaviorData item : behaviorData) {
-        if (item == null) {
+    LocalDate windowStart = startDate;
+    while (!windowStart.isAfter(endDate)) {
+      LocalDate windowEnd = windowStart.plusDays(API_WINDOW_DAYS - 1L);
+      if (windowEnd.isAfter(endDate)) windowEnd = endDate;
+      long startTime = windowStart.atStartOfDay(CHINA_ZONE).toEpochSecond();
+      long endTime = windowEnd.plusDays(1).atStartOfDay(CHINA_ZONE).toEpochSecond() - 1;
+
+      for (int start = 0; start < followUsers.size(); start += BATCH_SIZE) {
+        List<String> batchUsers = followUsers.subList(start, Math.min(start + BATCH_SIZE, followUsers.size()));
+        WecomUserBehaviorDataResponse response =
+            wecomClient.getStudentContactBehaviorData(batchUsers, startTime, endTime);
+        List<WecomUserBehaviorDataResponse.BehaviorData> behaviorData = response.behaviorData();
+        if (behaviorData == null) {
           continue;
         }
-        int itemChatCount = value(item.chatCnt());
-        int itemMessageCount = value(item.messageCnt());
-        newApplyCount += value(item.newApplyCnt());
-        newContactCount += value(item.newContactCnt());
-        chatCount += itemChatCount;
-        messageCount += itemMessageCount;
-        negativeFeedbackCount += value(item.negativeFeedbackCnt());
-        if (item.replyPercentage() != null && itemChatCount > 0) {
-          replyPercentageWeightedSum += item.replyPercentage() * itemChatCount;
-          replyPercentageWeight += itemChatCount;
-        }
-        if (item.avgReplyTime() != null && itemMessageCount > 0) {
-          avgReplyTimeWeightedSum += item.avgReplyTime() * itemMessageCount;
-          avgReplyTimeWeight += itemMessageCount;
+        for (WecomUserBehaviorDataResponse.BehaviorData item : behaviorData) {
+          if (item == null) continue;
+          int itemChatCount = value(item.chatCnt());
+          int itemMessageCount = value(item.messageCnt());
+          newApplyCount += value(item.newApplyCnt());
+          newContactCount += value(item.newContactCnt());
+          chatCount += itemChatCount;
+          messageCount += itemMessageCount;
+          negativeFeedbackCount += value(item.negativeFeedbackCnt());
+          if (item.replyPercentage() != null && itemChatCount > 0) {
+            replyPercentageWeightedSum += item.replyPercentage() * itemChatCount;
+            replyPercentageWeight += itemChatCount;
+          }
+          if (item.avgReplyTime() != null && itemMessageCount > 0) {
+            avgReplyTimeWeightedSum += item.avgReplyTime() * itemMessageCount;
+            avgReplyTimeWeight += itemMessageCount;
+          }
         }
       }
+      windowStart = windowEnd.plusDays(1);
     }
 
     Integer replyPercentage = replyPercentageWeight == 0 ? null
@@ -155,21 +164,29 @@ public class WecomStudentContactStatsService {
         negativeFeedbackCount, replyPercentage, avgReplySeconds);
   }
 
-  private GroupMessageSummary fetchGroupMessageSummary(long startTime, long endTime) {
+  private GroupMessageSummary fetchGroupMessageSummary(LocalDate startDate, LocalDate endDate) {
     try {
       Set<String> messageIds = new HashSet<>();
-      String cursor = "";
-      while (true) {
-        WecomGroupMessageListResponse response =
-            wecomClient.getCustomerGroupMessages(startTime, endTime, cursor, BATCH_SIZE);
-        if (response.groupMessageList() != null) {
-          response.groupMessageList().stream()
-              .filter(item -> item != null && item.msgid() != null && !item.msgid().isBlank())
-              .map(WecomGroupMessageListResponse.GroupMessage::msgid)
-              .forEach(messageIds::add);
+      LocalDate windowStart = startDate;
+      while (!windowStart.isAfter(endDate)) {
+        LocalDate windowEnd = windowStart.plusDays(API_WINDOW_DAYS - 1L);
+        if (windowEnd.isAfter(endDate)) windowEnd = endDate;
+        long startTime = windowStart.atStartOfDay(CHINA_ZONE).toEpochSecond();
+        long endTime = windowEnd.plusDays(1).atStartOfDay(CHINA_ZONE).toEpochSecond() - 1;
+        String cursor = "";
+        while (true) {
+          WecomGroupMessageListResponse response =
+              wecomClient.getCustomerGroupMessages(startTime, endTime, cursor, BATCH_SIZE);
+          if (response.groupMessageList() != null) {
+            response.groupMessageList().stream()
+                .filter(item -> item != null && item.msgid() != null && !item.msgid().isBlank())
+                .map(WecomGroupMessageListResponse.GroupMessage::msgid)
+                .forEach(messageIds::add);
+          }
+          cursor = response.nextCursor();
+          if (cursor == null || cursor.isBlank()) break;
         }
-        cursor = response.nextCursor();
-        if (cursor == null || cursor.isBlank()) break;
+        windowStart = windowEnd.plusDays(1);
       }
 
       int targets = 0;
diff --git a/src/test/java/com/company/agentfoundation/integration/wecom/service/WecomStudentContactStatsServiceTest.java b/src/test/java/com/company/agentfoundation/integration/wecom/service/WecomStudentContactStatsServiceTest.java
index b318e9c..8dda32c 100644
--- a/src/test/java/com/company/agentfoundation/integration/wecom/service/WecomStudentContactStatsServiceTest.java
+++ b/src/test/java/com/company/agentfoundation/integration/wecom/service/WecomStudentContactStatsServiceTest.java
@@ -21,6 +21,8 @@ import static org.mockito.ArgumentMatchers.anyLong;
 import static org.mockito.ArgumentMatchers.anyString;
 import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
 class WecomStudentContactStatsServiceTest {
@@ -67,4 +69,23 @@ class WecomStudentContactStatsServiceTest {
     assertEquals(0.3333D, stats.groupReachRate());
     assertTrue(stats.groupStatsAvailable());
   }
+
+  @Test
+  void splitsThirtyOneDayMonthIntoTwoApiWindows() {
+    WecomClient client = mock(WecomClient.class);
+    when(client.getStudentContactFollowUsers())
+        .thenReturn(new WecomFollowUserListResponse(0, "ok", List.of("employee-1")));
+    when(client.batchGetStudentContacts(eq(List.of("employee-1")), anyString(), anyInt()))
+        .thenReturn(new WecomExternalContactBatchResponse(0, "ok", List.of(), ""));
+    when(client.getStudentContactBehaviorData(eq(List.of("employee-1")), anyLong(), anyLong()))
+        .thenReturn(new WecomUserBehaviorDataResponse(0, "ok", List.of()));
+    when(client.getCustomerGroupMessages(anyLong(), anyLong(), anyString(), anyInt()))
+        .thenReturn(new WecomGroupMessageListResponse(0, "ok", List.of(), ""));
+
+    new WecomStudentContactStatsService(client).fetchStats(
+        LocalDate.of(2026, 5, 1), LocalDate.of(2026, 5, 31));
+
+    verify(client, times(2)).getStudentContactBehaviorData(eq(List.of("employee-1")), anyLong(), anyLong());
+    verify(client, times(2)).getCustomerGroupMessages(anyLong(), anyLong(), anyString(), anyInt());
+  }
 }