diff --git a/CHANGES.md b/CHANGES.md
index 9593314e2d..2c3e30831f 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -30,6 +30,8 @@ Release Notes.
 
 #### Documentation
 
+* update backend-alarm.md doc, support op "=" to "==".
+
 All issues and pull requests are [here](https://github.com/apache/skywalking/milestone/112?closed=1)
 
 ------------------
diff --git a/docs/en/setup/backend/backend-alarm.md b/docs/en/setup/backend/backend-alarm.md
index f6e778233c..c19bf94d08 100644
--- a/docs/en/setup/backend/backend-alarm.md
+++ b/docs/en/setup/backend/backend-alarm.md
@@ -40,7 +40,7 @@ The four label settings mentioned above must implement `LabeledValueHolder`.*
 For multiple-value metrics, such as **percentile**, the threshold is an array. It is described as:  `value1, value2, value3, value4, value5`.
 Each value may serve as the threshold for each value of the metrics. Set the value to `-` if you do not wish to trigger the alarm by one or more of the values.  
 For example in **percentile**, `value1` is the threshold of P50, and `-, -, value3, value4, value5` means that there is no threshold for P50 and P75 in the percentile alarm rule.
-- **OP**. The operator. It supports `>`, `>=`, `<`, `<=`, `=`. We welcome contributions of all OPs.
+- **OP**. The operator. It supports `>`, `>=`, `<`, `<=`, `==`. We welcome contributions of all OPs.
 - **Period**. The size of metrics cache in minutes for checking the alarm conditions. This is a time window that corresponds to the backend deployment env time.
 - **Count**. Within a period window, if the number of times which **value** goes over the threshold (based on OP) reaches `count`, then an alarm will be sent.
 - **Only as condition**. Indicates if the rule can send notifications, or if it simply serves as an condition of the composite rule.