If the foundation is not very good, it is recommended to use From Textbook to Olympiad Mathematics, produced by East China Normal University. This set of books closely follows the progress of classroom teaching, and selects typical and moderately difficult questions from each class to explain and train, so that students can master textbook knowledge skillfully. At the same time, from shallow to deep, gradually transition to the relevant content of the game, from the middle and low difficulty problems in the game, quickly reach the introduction of the game. I have been letting students use this set of books, and the effect is very good. They are no longer afraid of math and olympiad, they are full of confidence.

If you have a good foundation, you can use the blue-covered Olympic math course, which is very classic.