Mixer is an indispensable part in electronic communication system, and is the front-end circuit of heterodyne receiver and microwave measuring instrument. Whether it is microwave communication, radar and many microwave measurement systems, the microwave signal must be mixer down to IF for processing. With the development of optical communication, optical mixer in coherent optical communication plays an important role in coherent receiving terminal and optical measurement system. This paper starts with the electric mixer, expounds the principle and development status of the optical mixer, and briefly introduces the work of Xi′an University of Technology in the field of optical mixer, and prospects the development trend and prospects of mixer in the future.