In this paper, a model for the photocurrent of the quantum dot infrared photodetector (QDIP) including the continuous potential distribution of the electrons and the total electron transport is improved with the consideration of the dependence of the photoconductive gain on the applied bias, and this improved model can be further used to estimate the responsivity of the photodetector. The corresponding calculated results show a good agreement with the published results, which verifies the validity of the improved model.