I'm getting this laptop and it's got windows 8.1 can sims 3 work on that?

Yeah it depends on the user you have several options to make sims 3 work. You can run the program in compatibility mode, meaning you can right click the program go to properties and click compatibility tab and select a version below windows 8 e.g windows 7 or something like that. Or you could try wrapping your driver to run older games. That is a lengthier explanation and your best bet is to search it up. But in answer yea it should work.