During the process of studying functions, we are faced with all kinds of questions, such as determination of the domain of function and range as well as monotone interval, calculation of the value of function, proof tests and so on. If we only analysis functional equations, it will turn out to be difficult and confusable. However, the idea of number-form combination is quite effective. It solve number problem by form and solve problem form by number, exhibiting abstract problem by visualized graphics, which is the specification for abstract issues and substantiation for ambiguity. By simplification for complicated problem, we can deal with problem efficiently. This paper will discuss the usage of function concept with several examples to show the core of the idea of number-form combination. During the process of studying functions, we are faced with all kinds of questions, such as determination of the domain of function and range as well as monotone interval, calculation of the value of function, proof tests and so on. If we only analysis functional equations, it will turn out to be difficult and confusable. However, the idea of number-form combination is quite effective. It solve number problem by form and solve problem form by number, exhibiting abstract problem by visualized graphics, which is the specification for abstract issues and substantiation for ambiguity. By simplification for complicated problem, we can deal with problem efficiently. This paper will discuss the usage of function concept with several examples to show the core of the idea of number-form combination.