diff --git a/hertzbeat-alerter/src/main/java/org/apache/hertzbeat/alert/reduce/AlarmGroupReduce.java b/hertzbeat-alerter/src/main/java/org/apache/hertzbeat/alert/reduce/AlarmGroupReduce.java
index fac5f7b268f..79c9b73493e 100644
--- a/hertzbeat-alerter/src/main/java/org/apache/hertzbeat/alert/reduce/AlarmGroupReduce.java
+++ b/hertzbeat-alerter/src/main/java/org/apache/hertzbeat/alert/reduce/AlarmGroupReduce.java
@@ -291,7 +291,9 @@ private void sendGroupAlert(GroupAlertCache cache) {
         // For firing alerts, check repeat interval
         if (CommonConstants.ALERT_STATUS_FIRING.equals(status)) {
             AlertGroupConverge ruleConfig = groupDefines.get(cache.getGroupDefineName());
-            long repeatInterval = ruleConfig.getRepeatInterval() != null
+            // The rule may have been deleted, renamed or disabled while this group cache
+            // still holds firing alerts; fall back to the default interval like shouldSendGroup.
+            long repeatInterval = ruleConfig != null && ruleConfig.getRepeatInterval() != null
                     ? ruleConfig.getRepeatInterval() * MS_PER_SECOND : DEFAULT_REPEAT_INTERVAL;
 
             // Skip if within repeat interval. The throttle only suppresses repeated firing
diff --git a/hertzbeat-alerter/src/test/java/org/apache/hertzbeat/alert/reduce/AlarmGroupReduceTest.java b/hertzbeat-alerter/src/test/java/org/apache/hertzbeat/alert/reduce/AlarmGroupReduceTest.java
index 4611d521383..519a3221e49 100644
--- a/hertzbeat-alerter/src/test/java/org/apache/hertzbeat/alert/reduce/AlarmGroupReduceTest.java
+++ b/hertzbeat-alerter/src/test/java/org/apache/hertzbeat/alert/reduce/AlarmGroupReduceTest.java
@@ -37,6 +37,7 @@
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
+import java.lang.reflect.Field;
 import org.apache.hertzbeat.alert.dao.AlertGroupConvergeDao;
 import org.apache.hertzbeat.common.config.VirtualThreadProperties;
 import org.apache.hertzbeat.common.entity.alerter.AlertGroupConverge;
@@ -212,6 +213,37 @@ void whenMemberRecoversInsideRepeatInterval_recoveryMustStillBeEmitted() {
                 "memory recovery was silently dropped by the firing repeat-interval throttle");
     }
 
+    /**
+     * Regression: deleting (or renaming/disabling) a converge rule while its group cache still
+     * holds a firing alert must not break the periodic group dispatch with an NPE. The orphaned
+     * group has to fall back to the default repeat interval, like shouldSendGroup already does
+     * for the group wait/interval.
+     */
+    @Test
+    void whenRuleDeleted_firingGroupCacheMustStillBeDispatched() throws Exception {
+        alarmGroupReduce.refreshGroupDefines(Collections.singletonList(groupRule()));
+
+        alarmGroupReduce.processGroupAlert(alert("cpu", "firing", "host1"));
+
+        // The rule is deleted or disabled; refresh loads only enabled rules, orphaning the cache.
+        alarmGroupReduce.refreshGroupDefines(Collections.emptyList());
+
+        // Age the cache past the default group wait so the periodic check picks the group up.
+        Field cachesField = AlarmGroupReduce.class.getDeclaredField("groupCacheMap");
+        cachesField.setAccessible(true);
+        Map<?, ?> caches = (Map<?, ?>) cachesField.get(alarmGroupReduce);
+        for (Object cache : caches.values()) {
+            Field createTimeField = cache.getClass().getDeclaredField("createTime");
+            createTimeField.setAccessible(true);
+            createTimeField.setLong(cache, System.currentTimeMillis() - 60_000);
+        }
+
+        alarmGroupReduce.runCheckAndSendGroups();
+
+        verify(alarmInhibitReduce, atLeastOnce()).inhibitAlarm(argThat(group ->
+                group.getAlerts().stream().anyMatch(a -> "cpu".equals(a.getFingerprint()))));
+    }
+
     private AlertGroupConverge groupRule() {
         AlertGroupConverge rule = new AlertGroupConverge();
         rule.setName("test-rule");