This paper studies the application of C language graphic function in the computer design process through rna practical example of menu design using C language. It consists of three main modules:the instruction of rnself-definition function used in the process of initialization of screen and menu system, the instruction of inirntialization screen and menu system, and the instruction of self-definition function used in keyboard service rnprogram. The study reveals the properties of abundance and practice of the library function of C language.