diff --git a/src/dns_cache.c b/src/dns_cache.c
index 6434548..aaf2479 100644
--- a/src/dns_cache.c
+++ b/src/dns_cache.c
@@ -72,6 +72,10 @@ int dns_cache_replace(char *domain, char *cname, int cname_ttl, int ttl, dns_typ
 		return 0;
 	}
 
+	if (ttl < DNS_CACHE_TTL_MIN) {
+		ttl = DNS_CACHE_TTL_MIN;
+	}
+
 	dns_cache->ttl = ttl;
 	dns_cache->qtype = qtype;
 	dns_cache->ttl = ttl;
@@ -125,12 +129,17 @@ int dns_cache_insert(char *domain, char *cname, int cname_ttl, int ttl, dns_type
 		goto errout;
 	}
 
+	if (ttl < DNS_CACHE_TTL_MIN) {
+		ttl = DNS_CACHE_TTL_MIN;
+	}
+
 	key = hash_string(domain);
 	key = jhash(&qtype, sizeof(qtype), key);
 	strncpy(dns_cache->domain, domain, DNS_MAX_CNAME_LEN);
 	dns_cache->cname[0] = 0;
 	dns_cache->qtype = qtype;
 	dns_cache->ttl = ttl;
+	dns_cache->hitnum = 6;
 	atomic_set(&dns_cache->ref, 1);
 	time(&dns_cache->insert_time);
 	if (qtype == DNS_T_A) {
@@ -247,6 +256,7 @@ void dns_cache_update(struct dns_cache *dns_cache)
 	if (!list_empty(&dns_cache->list)) {
 		list_del_init(&dns_cache->list);
 		list_add_tail(&dns_cache->list, &dns_cache_head.cache_list);
+		dns_cache->hitnum++;
 	}
 	pthread_mutex_unlock(&dns_cache_head.lock);
 }
diff --git a/src/dns_cache.h b/src/dns_cache.h
index 5d12efc..de6d28b 100644
--- a/src/dns_cache.h
+++ b/src/dns_cache.h
@@ -8,6 +8,8 @@
 #include "list.h"
 #include <time.h>
 
+#define DNS_CACHE_TTL_MIN 30
+
 struct dns_cache {
 	struct hlist_node node;
 	struct list_head list;
@@ -17,6 +19,7 @@ struct dns_cache {
 	char cname[DNS_MAX_CNAME_LEN];
 	unsigned int cname_ttl;
 	unsigned int ttl;
+	int hitnum;
 	time_t insert_time;
 	dns_type_t qtype;
 	union {
diff --git a/src/dns_server.c b/src/dns_server.c
index 736448e..1feda76 100644
--- a/src/dns_server.c
+++ b/src/dns_server.c
@@ -1865,7 +1865,13 @@ void _dns_server_tcp_ping_check(struct dns_request *request)
 
 void _dns_server_prefetch_domain(struct dns_cache *dns_cache)
 {
-	tlog(TLOG_DEBUG, "prefetch by cache %s, qtype %d, ttl %d", dns_cache->domain, dns_cache->qtype, dns_cache->ttl);
+	if (dns_cache->hitnum <= 0) {
+		return;
+	}
+
+	dns_cache->hitnum--;
+
+	tlog(TLOG_DEBUG, "prefetch by cache %s, qtype %d, ttl %d, hitnum %d", dns_cache->domain, dns_cache->qtype, dns_cache->ttl, dns_cache->hitnum);
 	if (_dns_server_prefetch_request(dns_cache->domain, dns_cache->qtype) != 0) {
 		tlog(TLOG_ERROR, "prefetch domain %s, qtype %d, failed.", dns_cache->domain, dns_cache->qtype);
 	}