Abstract: An InP/In0.53Ga0.47As/InP infrared photocathode model was established. The In0.53Ga0.47As absorber layer was designed as a multi-layer structure, the impurities of it were exponentially distributed by doping with different concentrations of the thin layers. The one-dimensional continuity equations and boundary conditions of the photoelectron in the absorber layer and the emissive layer were given and the probability that photoelectrons overcome the launch of the active layer barrier into the vacuum was calculated. The effects of absorber layer thickness, doping concentration and cathode bias voltage on the internal quantum efficiency of the cathode was simulated under the condition of picosecond response time, and then the law of the external quantum yield of the cathode was obtained with the above three factors. The results show that, when the doping concentration of the absorber layer changes within the range of 1015-1018 cm-3, The internal quantum efficiency change is very small; as the thickness of the absorber layer increases within 0.09-0.81 m, the internal quantum efficiency increases. As the external bias voltage increases, the internal quantum efficiency increases first and then tends to be stable. A set of cathode design parameters that could achieve both high quantum efficiency and fast time response were presented. Theoretically, an external quantum yield of 8.4% can be obtained for 1.55 m incident light, and the response time is 49 ps.