sometimes my macbook air fan is very louder, and always crash and can not turn it off

Hello and welcome to Apple Support Communities, Vkwj58!

I understand your MacBook Air fans run loud and also it cannot be shut off. I'd be happy to provide information to help you troubleshoot this.

Use the steps in the following articles:

How to reset the System Management Controller (SMC) on your Mac

If your Mac restarted because of a problem

Have a great day!