3D imaging LADAR based on APD arrays captures 3D image with single laser pulse.In order to emulate and evaluate the system performance,the signal-to-noise (SNR)and probability of detection (Pd)vs.the gain and threshold voltage of APD arrays were discussed in this paper.And t1he simulation results indicate that selecting an appropriate gain of APD arrays,the SNR and Pd can achieve the maximum;as threshold voltage of detector arrays increasing,it will reduce the probability of detection with a great influence.