Why my computer will suddenly turned off when playing high graphic games?

what temps

what specs including make and model of power supply.

Help us to help you.

It's usually a power supply issue or a heating one. Try monitoring the temperatures under load and if having a spare power supply, connect it and test.

1- Heating -- try clean up dust inside the case, fans, etc.

2- Power Supply -- perhaps it does not delivery enough power to your graphic card under heavy load, or it is diying.

Your computer is likely not up to specifications.
Make sure you check before you buy games to see whether or not you can play them.
Just because you meet the minimum does not mean you can always play them easily. At least aim for having the recommended parts.
----------------
If upgrading is out of the question, making sure you have proper air flow, and no dust in your computer can go a long way.
A good investment is a heavy duty air compressor.
Works EXTREMELY well for cleaning computer parts.