If it is Beijing, the Department of Mathematics of Peking University is the best, followed by Tsinghua. Of course, these two schools are more difficult to test. Compared with Beijing University of Posts and Telecommunications, the Department of Mathematics is really similar. However, the communication major of Beihou University is still fierce, and the mathematics department is average. I am a graduate of Beijing University of Posts and Telecommunications and have a general understanding of the Department of Mathematics, but I suggest you consider Beijing University of Posts and Telecommunications. Students here will have a slight advantage over Beijing University of Posts and Telecommunications in finding jobs in the future, especially in the communication and IT industries.