Although people in China say that they are good at math, graduate education lags behind foreign countries for ten years or even longer.

I only know some graph theory. Professor Bollbas from Cambridge and the University of Waterloo in Canada are all good choices. Professor N. Alon is also an authority in this field. If you want to go abroad to teach with a China person, Professor Du Dingchu and Professor Zhang Cunquan from the United States are also very good. Please check their specific school.