A photon counting imaging lidar system with four Geiger-mode avalanche photodiode(Gm-APD) detectors was proposed. A 2×2 optical fiber array was used in the system to receive echo pulse simultaneously. The distance of the target was obtained through the signals of the four channels in real time. The detection probability, the false alarm probability and the range accuracy of the lidar system were calculated. Comparing with the single Gm-APD system, the detection performances were all significantly improved the detection probability was improved from 60.6% to 91.6%, the false alarm probability was restrained from 1.9% to 0.2%，and the range accuracy was improved from 1.771 m to 0.440 m. By mean of the 64×64 pixels range imaging simulations of the single Gm-APD system and the approach in this paper, the validity of the theoretical derivation is demonstrated.