I want to write a thesis statement on the topic "China is not going to be the next superpower" How am i supposed to write it?

Your thesis statement must include factual information plus your position/opinion/stance, both of which are in that sentence. If you want to make it a stronger thesis, go here:

http://leo.stcloudstate.edu/acadwrite/thesistatement.html

This is one of the very best places I've seen online to help students write good thesis statements. Study all the examples they give, especially the last one. It shows you how to end up with a basic thesis statement (which you have) and some ideas about what you'll include in your argument.