diff --git a/alert/README.md b/alert/README.md
index 547f3a0381a74714b1f6c8c74b861678b3805619..b8b8c92a2797bf58ca9f80b1781fc1f5d7555f6b 100644
--- a/alert/README.md
+++ b/alert/README.md
@@ -61,7 +61,7 @@ The use of each configuration item is:
 
 * **port**: This is the `http` service port which enables other application to manage rules by `restful API`.
 * **database**: rules are stored in a `sqlite` database, this is the path of the database file (if the file does not exist, the alert application creates it automatically).
-* **tdengine**: connection string of `TDEngine` server, note the database name should be put in the `sql` field of a rule in most cases, thus it should NOT be included in the string.
+* **tdengine**: connection string of `TDEngine` server (please refer the documentation of GO connector for the detailed format of this string), note the database name should be put in the `sql` field of a rule in most cases, thus it should NOT be included in the string.
 * **log > level**: log level, could be `production` or `debug`.
 * **log > path**: log output file path.
 * **receivers > alertManager**: the alert application pushes alerts to `AlertManager` at this URL.
diff --git a/alert/README_cn.md b/alert/README_cn.md
index 938b23a58406f5d6f279191a47dc957c446911ce..f659e997e3ea8ec8acef8cc3eb6e41a4c692a476 100644
--- a/alert/README_cn.md
+++ b/alert/README_cn.md
@@ -58,7 +58,7 @@ $ go build
 
 * **port**：报警监测程序支持使用 `restful API` 对规则进行管理，这个参数用于配置 `http` 服务的侦听端口。
 * **database**：报警监测程序将规则保存到了一个 `sqlite` 数据库中，这个参数用于指定数据库文件的路径（不需要提前创建这个文件，如果它不存在，程序会自动创建它）。
-* **tdengine**：`TDEngine` 的连接字符串，一般来说，数据库名应该在报警规则的 `sql` 语句中指定，所以这个字符串中 **不** 应包含数据库名。
+* **tdengine**：`TDEngine` 的连接字符串（这个字符串的详细格式说明请见 GO 连接器的文档），一般来说，数据库名应该在报警规则的 `sql` 语句中指定，所以这个字符串中 **不** 应包含数据库名。
 * **log > level**：日志的记录级别，可选 `production` 或 `debug`。
 * **log > path**：日志文件的路径。
 * **receivers > alertManager**：报警监测程序会将报警推送到 `AlertManager`，在这里指定 `AlertManager` 的接收地址。
diff --git a/alert/app/rule.go b/alert/app/rule.go
index 44596ca26d7da0ddec55dfabc2930c7166dc3547..236e5bd75562d90cac8bb5e20608dc08e1298f56 100644
--- a/alert/app/rule.go
+++ b/alert/app/rule.go
@@ -84,6 +84,7 @@ func (alert *Alert) doRefresh(firing bool, rule *Rule) bool {
 
 	case firing && (alert.State == AlertStateWaiting):
 		alert.StartsAt = time.Now()
+		alert.EndsAt = time.Time{}
 		if rule.For.Nanoseconds() > 0 {
 			alert.State = AlertStatePending
 			return false
@@ -95,6 +96,7 @@ func (alert *Alert) doRefresh(firing bool, rule *Rule) bool {
 			return false
 		}
 		alert.StartsAt = alert.StartsAt.Add(rule.For.Duration)
+		alert.EndsAt = time.Time{}
 		alert.State = AlertStateFiring
 
 	case firing && (alert.State == AlertStateFiring):