Abstract: Laser detection and ranging system based on Geiger-mode APD (GM-APD) array can achieve very high sensitivity, spatial resolution and ranging precision, which has wide applications in remote sensing, target recognition and so on. Limited by the factors of detection mode and noises, GM-APD usually requires large number of photon detections to carry out high imaging precise. For this problem, firstly a ladar system based on national state-of-the-art InGaAs GM-APD array was set up at a wavelength of 1 064 nm. The system was then used for imaging of a building about 600 m away. The photon detection process on GM-APD was analyzed for the reflection and ranging information extractions with maximum likelihood estimation method. For the condition that only a few photons were detected on a pixel, the prior of natural scene’s spare property was used to improve the imaging precise based on regularized image reconstruction method. Through comparison, it was verified that the regularized method can reduce the estimation error due to photon detection fluctuation, and improve the imaging quality.