Update README.md
diff --git a/6/6.3/oap/README.md b/6/6.3/oap/README.md
index c062478..7ef3348 100644
--- a/6/6.3/oap/README.md
+++ b/6/6.3/oap/README.md
@@ -23,6 +23,9 @@
We could set up environment variables to configure this image. Most of them are defined in [backend-setup](https://github.com/apache/skywalking/blob/v6.3.0/docs/en/setup/backend/backend-setup.md), but Apache SkyWalking Docker Image adds extra environment variables to help the user to compose it properly. The details are located in [docker-entrypoint.sh](docker-entrypoint.sh)
+## SW_ENVOY_ALS_ENABLED
+No default value, set it to `true` to open ALS solution of SkyWalking.
+
## SW_CLUSTER
Default value is `standalone`, avaliable values are:
