This paper briefly introduces the principles of determining the contents of compulsory courses and elective courses in "Mathematics Curriculum Standards for Ordinary Senior High Schools (Experiments)". A: The principle of determining the content of compulsory courses is to meet the basic mathematics needs of future citizens and provide necessary mathematics preparation for students' further study. The principle of determining the content of elective courses is to meet students' interests and future development needs, and to lay the foundation for students to further study and obtain higher mathematics literacy. Among them, the L series is for students who want to develop in humanities and social sciences, and the 2 series is for students who want to develop in science, engineering and economics. L series and 2 series are the basic contents of elective courses. Series 3 and 4 are designed for students who are interested in mathematics and want to further improve their mathematics literacy. The content involved reflects some important mathematical ideas, which is helpful for students to further lay a good foundation in mathematics, improve their application awareness, help students develop for life, broaden their horizons in mathematics, and improve their understanding of the scientific value, application value and cultural value of mathematics.