The idea of function is to analyze and study the quantitative relationship in specific problems from the viewpoint of movement change, establish the functional relationship, and use the knowledge of function to solve problems. This way of thinking lies in revealing the essential characteristics of the quantitative relationship of problems, paying attention to the dynamic study of problem variables, and broadening the thinking of solving problems from the perspective of the movement, change, connection and development of variables. Specifically, the idea of function is as follows: (1) The idea of "universal connection" is that the world is universally connected and all quantities are always interdependent. (2) Seeking "regularity" (relational expression) in "change", that is, the idea of "patterning". (3) Pursuing the ideas of order, structure and symmetry in law. (4) I feel that "change" is fast and slow, sometimes the speed of change is fixed and sometimes it changes. (5) according to the "law" to judge the development trend, predict the future, grasp the future.