Negative electron affinity GaN photocathode with greatly advanced photoelectricity performance is described. The research of GaN photocathode focuses on the three points, i. e. , quantum yield, electron energy distribution and surface model, in the last decade. The domestic research of GaN photocathode is still in its infancy, the basic theory is not established, and preparation technology is not mature. In this paper we review emission mechanism, material growth, surface cleaning, activation process optimization, varied-doping structure design and stability of GaN photocathode. The latest experimental results confirm that the fabrication technology of GaN photocathode is feasible.