In the teaching process of elementary school mathematics, it is necessary to make careful presuppositions, because mathematics teaching is firstly for teachers to carry out purposeful and planned teaching activities. Teachers must review the teaching objectives, important and difficult points and teaching links of this lesson before class. There is a clear and scientific arrangement. But at the same time, this kind of meticulous pre-class pre-setting is flexible. There must be room for blank space. The ultimate goal of pre-setting is to complete the teaching goal.