Now it is the new curriculum teaching, emphasizing and highlighting students' subjectivity, and adopting "cooperation, autonomy and inquiry" learning to give students more independent learning space. Therefore, how to make full use of classroom time, arouse students' enthusiasm and improve classroom efficiency is an important problem for math teachers. In teaching, I think if there is a good tutor in class, it will attract students' attention, stimulate students' interest and make students concentrate on class. Because "a good beginning is half the battle", and a good lead design often plays the role of "... she turned the tuning pin, tested several strings, and even before she played, we could feel her feelings. Lead-in is very important in the whole classroom teaching. It is like a bridge connecting old lessons with new knowledge. As a prelude, it indicates the climax and ending behind; Like a road sign, it points out the thinking direction of students; Just as the prelude of music lays the foundation for the whole classroom, whether it is high or dull, the author thinks that there are at least the following basic principles to follow in how to design the introduction in senior high school mathematics classroom.