I have a 2001 chevy malibu and the check engine light is on because of the gas cap. I have change it a few time and found one that worked but it only lasted for about 30 days and the light came back on. How can I get the light to stay off

You find out why the cap goes bad in only 30 days and fix that. There is something else wrong.. lke a damaged fuel filler neck. That is destrying the fuel cap seals.

What is the code? An EVAP code will SOMETIMES only be a gas cap but it could be a leak in the EVAP system. A pinhole leak somewhere in the system will often throw the code and the first answer, because it is the most simple and cheapest, is to replace the gas cap. You probably need to take your car somewhere and have a smoke test done on it.

Had same problem. Replaced filler pipe. Was rotting out.

Chuck