The photocurrent curves of reflection-mode GaAs photocathodes as a function of time, when were illuminated by white light with an intensity of 0, 33 and 100lx, respectively, were measured using a multi-information measurement system. The calculated lifetimes of cathodes are 320, 160 and 75min, respectively, showing that the stability of cathodes degraded with the increase of light intensity. The lifetime of cathode, illuminated by white light with an intensity of 100lx, while no photocurrent was being drawn during the illumination, was 100min. Through comparison, we found that the influence of illumination on cathodes stability is greater than that of photocurrent. The quantum-yield curves of cathodes as a functions of time, when illuminated by white light with an intensity of 33lx, were measured also. The measured results show that the shape of the yield curves changes with increasing illumination time due to the faster quantum-yield degradation rate of low energy photons. Based on the revised quantum-efficiency equations for the reflection-mode cathodes, the variation of yield curves are analyzed to be due to the intervalley diffusion of photoelectrons and the evolution of the surface potential barrier profile of the photocathodes during degradation process.