diff --git a/tencentcloud/services/crs/resource_tc_redis_instance.go b/tencentcloud/services/crs/resource_tc_redis_instance.go
index 6b6bd7e3d8..dac712dae4 100644
--- a/tencentcloud/services/crs/resource_tc_redis_instance.go
+++ b/tencentcloud/services/crs/resource_tc_redis_instance.go
@@ -118,8 +118,8 @@ func ResourceTencentCloudRedisInstance() *schema.Resource {
 			"mem_size": {
 				Type:         schema.TypeInt,
 				Required:     true,
-				ValidateFunc: tccommon.ValidateAllowedIntValue([]int{256, 1024, 2048, 4096, 8192, 12288, 16384, 20480, 24576, 32768, 40960, 49152, 65536}),
-				Description:  "The memory volume of an available instance(in MB), please refer to `tencentcloud_redis_zone_config.list[zone].shard_memories`. When redis is standard type, it represents total memory size of the instance; when Redis is cluster type, it represents memory size of per sharding.",
+				ValidateFunc: tccommon.ValidateAllowedIntValue([]int{256, 512, 1024, 2048, 4096, 8192, 12288, 16384, 20480, 24576, 32768, 40960, 49152, 65536}),
+				Description:  "The memory volume of an available instance(in MB), please refer to `tencentcloud_redis_zone_config.list[zone].shard_memories`. When redis is standard type, it represents total memory size of the instance; when Redis is cluster type, it represents memory size of per sharding. `512MB` is supported only in master-slave instance.",
 			},
 			"vpc_id": {
 				Type:         schema.TypeString,
diff --git a/website/docs/r/redis_instance.html.markdown b/website/docs/r/redis_instance.html.markdown
index d5efd6746a..92bb0fd037 100644
--- a/website/docs/r/redis_instance.html.markdown
+++ b/website/docs/r/redis_instance.html.markdown
@@ -239,7 +239,7 @@ resource "tencentcloud_redis_instance" "foo" {
 The following arguments are supported:
 
 * `availability_zone` - (Required, String, ForceNew) The available zone ID of an instance to be created, please refer to `tencentcloud_redis_zone_config.list`.
-* `mem_size` - (Required, Int) The memory volume of an available instance(in MB), please refer to `tencentcloud_redis_zone_config.list[zone].shard_memories`. When redis is standard type, it represents total memory size of the instance; when Redis is cluster type, it represents memory size of per sharding.
+* `mem_size` - (Required, Int) The memory volume of an available instance(in MB), please refer to `tencentcloud_redis_zone_config.list[zone].shard_memories`. When redis is standard type, it represents total memory size of the instance; when Redis is cluster type, it represents memory size of per sharding. `512MB` is supported only in master-slave instance.
 * `auto_renew_flag` - (Optional, Int, ForceNew) Auto-renew flag. 0 - default state (manual renewal); 1 - automatic renewal; 2 - explicit no automatic renewal.
 * `charge_type` - (Optional, String, ForceNew) The charge type of instance. Valid values: `PREPAID` and `POSTPAID`. Default value is `POSTPAID`. Note: TencentCloud International only supports `POSTPAID`. Caution that update operation on this field will delete old instances and create new with new charge type.
 * `force_delete` - (Optional, Bool) Indicate whether to delete Redis instance directly or not. Default is false. If set true, the instance will be deleted instead of staying recycle bin. Note: only works for `PREPAID` instance.