There exists various defects during the growth of large-size YAG crystals, and dislocation is one of the main defects. Dislocation can cause stress birefringence, decrease the optical uniformity, increase optical losses, shorten the work life of the crystal and so on, therefore, it is very important to grow YAG crystal without dislocation or with low dislocation for the development of high-efficiency solid-state laser. This paper summarizes the research progress of dislocation in YAG crystal at home and abroad in the recent 40 years, including the research on dislocation in YAG crystal by chemical etching method, the decoration method, synchrotron radiation method, stress birefringence method, X-ray micro tomography and light scattering tomography, as well as the application examples of TEM and SEM, and also introduces the effect of crystal growth process on dislocation density and distribution in crystal. It provides a reference for the dislocation research and the growth of large-size and high-quality YAG laser crystals.