Two books, Probability Theory and Mathematical Statistics, written by Zhejiang University and National University of Defense Technology, are well written, and both books are bought online. Mainly read Professor Wu Yi's books, Zhejiang University textbooks as reference books. If you don't understand one book, you can read the story of another book, and then combine the love course with the teacher's lecture video about the large-scale open online course. Basically understandable. The printed fonts of Zhejiang University books are thick and clear, while the latter fonts are slightly lighter.