I use the simple reason as i need to change school. Or you can use change a major or whatever. Plus you need get a letter from you advisor saying that you need a waiver to keep studying or whatever. To chinse embassy, the most important thing is the "agree" letter from China, and to department of state, is the No objection letter. The process is quite simple, takes around a year to my experience. All J students I know, as long as the univeristy in China agree to let go, No problem.
Good luck.