In order to investigate the decay tendency and the recovery status of the quantum efficiency of reflection-mode NEA GaN photocathode, the quantum efficiency curves have been studied after the photocathode was fully activated, stored in system and supplemented with Cs. The quantum efficiency decay and recovery processes of reflection-mode NEA GaN photocathode were observed and the mechanism was discussed. The quantum efficiency value of reflection-mode NEA GaN photocathode can be recovered up to more than 94% of the best value in the shortwave region between 240nm and 300nm, and more than 88% in the long wave region between 300nm and 375nm after Cs supplement. Based on the changes of surface potential barrier profiles of the reflection-mode NEA GaN photocathode before and after the quantum efficiency degradation and the quantum yield formula, the decay characteristic and the recovery status of quantum efficiency curve after supplement with Cs have been related to the changes of surface barrier shapes.