Thanks a lot for Webworkings' suggestion. I already checked the "Power Options" under "Control Panel". The setting for "Screen" off and "Sleep" is 1 hour without any activities with both "Battery" and "Plug in". So definitely it is not the Power Setting issue.
By the way the screen randomly off issue only happens just when the laptop is turn on to about 20~30 minutes. After that, it seems the laptop already warm-up, and the screen will no longer off randomly. I suspect it is hardware issue, but not sure which one: the screen itself, wire connection or the display circuit. I opened the laptop, all connection is fine, have not found anything abnormal. Another thing, the display on the external screen by selecting "Win key+ P" is always fine.
Sometimes my screen display has flickering issue, but all drivers are updated. The original storage is 512G hard disk, I upgraded it to 512G Samsung SSD driver with Samsung software(ghost all files in hard disk to SSD driver) when I bought the laptop two years ago.
Still work try to find the root cause.