I watched the video of Wang Xu, a senior teacher of Shijingshan Middle School in Shijingshan District, Beijing, about the connotation relationship and treatment of "presupposition" and "generation", and got a new understanding of the role of "presupposition and generation" in mathematics classroom teaching. "Presupposition" is prediction and design, and it is a teacher's purposeful and planned assumption and arrangement for teaching before class. "Generation" is growth and construction, and it is a new problem and situation that teachers and students exceed the teacher's preset plan in the interaction with teaching situation and teacher-student dialogue and interaction. Therefore, students' knowledge background, life experience and emotional experience should be fully considered in the teaching design under the new curriculum concept. In the process of knowledge learning, it is the key to stimulate students' interest in learning and guide them to actively explore by attracting students' active participation and handling the relationship between presupposition and generation. I designed a lesson in the teaching of Pythagorean Theorem: I prepared a tape measure, took the students to the playground, and asked them to get the backboard and the height of the teaching building from the PE teacher and the principal respectively, and then asked: A bird flew to the upper left corner of the teaching building in the upper right corner of the backboard. Please use the tape measure and the knowledge you have learned to find the shortest path for birds to fly (the backboard and the teaching building can't reach it). Students begin their activities. Some measure the horizontal distance from the top of the backboard to the top of the teaching building, and some draw geometric figures. Every student is very serious, and everyone is very happy and enjoys it. The classroom is full of harmony, pleasure and relaxation. This course not only trains students' mathematical "modeling" thought, but also allows students to experience the relationship between mathematics and life and production. Teaching should develop harmoniously in presupposition and generation. Only by building a harmonious bridge between teaching presupposition and dynamic generation can the fire of wisdom "passion" burn in classroom teaching.