As one of the two major units of measuring angles in trigonometric functions, the radian system has irreplaceable advantages and functions, and is widely used in mathematics and other scientific fields. This paper summarizes the history of the radian system for more than 300 years, and through the changes of the radian system in Chinese textbooks for more than 120 years from the end of the Qing Dynasty to the present, it is concluded that the radian system can make mathematical thinking economical and show the beauty of mathematics. At the same time, I give advice: I. Constantly improve the content setting of the radian system in the textbook; II. Further improve the teaching method of the radian system.