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 wide1spectral 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 1.5×1015cm-3and 1.0×1016cm-3respectively, 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. © 2016 spie.