GaN is becoming a promising material in ultraviolet detection and vacuum electronic source field for its good performance. High quantum efficiencies of greater than 70% and 30% have been achieved for the opaque mode and transparent mode GaN photocathode, respectively. This paper reviews the progress of GaN photocahtode in three important fields,including structure design, surface cleaning and Cs/O activation, analyzes the key factors influencing the quantum efficiency, and evaluates the prospect for its development.