The charge collection efficiency of electron bombarded active pixel sensor(EBAPS) was simulated while the EBAPS with uniformly doped P type substrate. The photoelectron scatting trajectories in dead layer and electron multiplier layer were simulated based on the low-energy electron-solid interaction model and Monte Carlo method. Meanwhile the influence factors how affecting the energy loss rate were studied. According to semiconductor theory, the influence factors(B atoms doping concentration, film thickness and the incident electron energy) how affecting the charge collection efficiency were studied. The final charge collection efficiency′s simulation results are consistent with the reported(4 keV, uniformly doping) measured results, which means the simulation result can provide theoretical guidance for the fabrication of high gain EBAPS.