The positive electron affinity potassium cesium antimony photocathode has driving laser wavelength is longer (532 nm), high quantum efficiency, long life, fast response time, in the field of electronic source has broad application potential, but limited by the photoelectric characteristics of the material itself, effective transport distance is very short, not enough to absorb all the incident light driven laser energy, and quantum efficiency is also affected. Therefore, this article introduced the Fabry-Perot cavity structure into the photocathode, to improve the effective absorption of incident driven laser, through the time domain finite difference method simulation study, make the active layer potassium cesium antimony light absorption reached 90%, and the reflective layer silver and dielectric layer silicon nitride were prepared and verified, predicted the quantum efficiency is 11.17%, to meet the requirements of high brightness, high frequency electron source in the future.