In this paper,the principle and features of four-wave mixing are given.The generation of four-wave mixing is derived in theory and the applications of four-wave mixing in the DWDM for optical fiber communication,phase conjugation wave generation and real time optical detection are given.The study in this paper is aimed at more completely knowing the application direction of the four-wave mixing, a typical nonlinear optical effect and finding more applications for the four-wave mixing by summing up the existing relatively mature applications and research methods.