The quantum efficiency characteristics of InP/In0.53Ga0.47As/InP photocathode which is one of the field-assisted negative electron affinity photocathodes with III-V compound semiconductor and works at transmission mode with a wide1 spectral response range from 1.0-1.7 μm were studied in this paper. Under certain field-assisted bias voltage, internal quantum efficiency at different wavelength versus structure parameters and doping concentration of the photocathode was simulated by the APSYS program. Results show that: First, internal quantum efficiency of the photocathode rises with the increasing of the field-assisted bias voltage. Second, the internal quantum efficiency gradually increases to a maximum at thickness=0.2um of P-InGaAs photo-absorbing layer and then reduces with the increasing of thickness. However, doping concentration of P-InGaAs photo-absorbing layer has little influence on it. Third, the internal quantum efficiency reduces with the increasing of thickness and doping concentration of P-InP photoelectron-emitting layer. The optimization results show that when the thickness of the photo-absorbing layer and the photoelectron-emitting layer are both 0.2 μm, and the doping concentration of the photo-absorbing layer and the photoelectron-emitting layer are about 1.5×1015 cm-3 and 1.0×1016 cm-3 respectively, under a certain field-assisted bias voltage, the line of the external quantum efficiency versus wavelength is ideal. Besides, the response time of photocathode can be reduced to less than 50 ps.