diff --git a/powerjob-common/src/main/java/com/github/kfcfans/powerjob/common/model/InstanceDetail.java b/powerjob-common/src/main/java/com/github/kfcfans/powerjob/common/model/InstanceDetail.java
index 90f12886..b14ab3dc 100644
--- a/powerjob-common/src/main/java/com/github/kfcfans/powerjob/common/model/InstanceDetail.java
+++ b/powerjob-common/src/main/java/com/github/kfcfans/powerjob/common/model/InstanceDetail.java
@@ -7,7 +7,7 @@ import lombok.NoArgsConstructor;
 import java.util.List;
 
 /**
- * 任务实例的运行详细信息
+ * Detailed info of task instances.
  *
  * @author tjq
  * @since 2020/4/11
@@ -24,7 +24,6 @@ public class InstanceDetail implements OmsSerializable {
      * Actual trigger time of an instance.
      */
     private Long actualTriggerTime;
-    // 任务整体结束时间（可能不存在）
     /**
      * Finish time of an instance, which may be null.
      */
@@ -49,30 +48,30 @@ public class InstanceDetail implements OmsSerializable {
      */
     private String instanceParams;
 
-    // MR或BD任务专用
     /**
      * Task detail, used by MapReduce or Broadcast tasks.
      */
     private TaskDetail taskDetail;
-    // 秒级任务专用
     /**
-     *
+     * Sub instance details, used by frequent tasks.
      */
     private List<SubInstanceDetail> subInstanceDetails;
 
-    // 重试次数
     /**
-     * 
+     * Running times.
      */
     private Long runningTimes;
 
-    // 扩展字段，中间件升级不易，最好不要再改 common 包了...否则 server worker 版本不兼容
     /**
-     * Extend
+     * Extended fields. Middlewares are not supposed to update frequently.
+     * Changes in PowerJob-common may lead to incompatible versions.
+     * PowerJob-common packages should not be modified if not necessary.
      */
     private String extra;
 
-    // 秒级任务的 extra -> List<SubInstanceDetail>
+    /**
+     * Extra info for frequent tasks, return List<SubInstanceDetail>.
+     */
     @Data
     @NoArgsConstructor
     public static class SubInstanceDetail implements OmsSerializable {
@@ -83,7 +82,9 @@ public class InstanceDetail implements OmsSerializable {
         private int status;
     }
 
-    // MapReduce 和 Broadcast 任务的 extra ->
+    /**
+     * Extra info of {@code MapReduce} or {@code Broadcast} type of tasks.
+     */
     @Data
     @NoArgsConstructor
     public static class TaskDetail implements OmsSerializable {
diff --git a/powerjob-common/src/main/java/com/github/kfcfans/powerjob/common/model/SystemMetrics.java b/powerjob-common/src/main/java/com/github/kfcfans/powerjob/common/model/SystemMetrics.java
index 7d053bbe..c90534f4 100644
--- a/powerjob-common/src/main/java/com/github/kfcfans/powerjob/common/model/SystemMetrics.java
+++ b/powerjob-common/src/main/java/com/github/kfcfans/powerjob/common/model/SystemMetrics.java
@@ -4,7 +4,7 @@ import com.github.kfcfans.powerjob.common.OmsSerializable;
 import lombok.Data;
 
 /**
- * Class for system metrics .
+ * Class for system metrics.
  *
  * @author tjq
  * @since 2020/3/25