The two-dimensional (2-D) simulations of p-i-n type InP/In0.53Ga0.47As/InP photodetector at low bias were presented. The modeling results fit the experimental results well, verifying the validity of our model and the desirability of the simulated results. In order to further optimize the detector structure, the effects of thickness and doping concentration of the absorption layer on the dark current and photoresponse were both simulated and discussed. One can find that the dark current doesn′t increase when the thickness of the absorption layer is over 0.3 μm. However, the photo-response increases as the thickness of the absorption layer increases. The dark current decreases monotonously as the doping concentration of the absorption layer increases, and when the doping concentration increases to 2×1017/cm3, the dark current reaches the lowest value. Finally, the transient time of photodetector is also simulated under different reverse bias, one can find that the response time can be decreased with the increase of the reverse voltage.