This paper introduces a method for analyzing the performance of laser radar based on Geiger-mode avalanche photodiode（APD）array.The detection probability,false-alarm probability and miss alarm probability are researched by analyzing the creation of primary photon electronics and dark count rate noise.Further more,the method of threshold detection with multiple-pulses are proposed，of which the detection probability and false probability are researched and simulated.For a target at a distance of 2 km to 10 km and the 128×128 Geiger-mode APD array,the detection probability of the ladar system can be improved as the pulse energy increasing,while the pulse energy should less than 200 mJ.When the pulse energy is above 200 mJ,the detection probability is constant.For the threshold detection with multiple-pulses,the detection probability of the ladar system can be improved as the pulse energy increasing,and the false-alarm probability can be reduced as the pulse energy increasing.