According to whether there is frequency difference between two laser beams locked by an optical phase-locked loop (OPLL), it can be divided into homodyne optical phase-locked loop and heterodyne optical phase-locked loop. The progress of heterodyne optical phase-locked loop was mainly introduced, which could keep the frequency difference between lasers relatively stable through frequency discrimination and phase discrimination. Compared with other laser offset locking methods, optical phase-locked loop has the advantages of simple structure, large servo bandwidth, wide offset range and high locking accuracy. It plays a very important role in atomic coherence, cold atom system, coherent beam combining, heterodyne interferometry and other fields, and has received more and more extensive attention. The main method of laser offset locking and the characteristics of optical phase-locked loop were introduced firstly, then the basic model of optical phase-locked loop was introduced, and the basic error model of optical phase-locked loop was analyzed. According to the different realization methods of OPLL, the key technologies and research progress of OPLL were introduced in detail. Then the application progress of OPLL in different fields in recent years was introduced. Finally, the development of this method was summarized and prospected.