In order to overcome the technical bottleneck which limits the increase of sensitivity of the low light level (LLL) image intensifier and the infrared imaging device, the photon counting technique is applied to the LLL imaging system, which can deduce the characteristics of the objects according to the number of the photon that the detector outputs. The avalanche photodiode (APD) is used for detector and is operated in Geiger mode. It is proved that APD has high sensitivity in the order of a single photon by analyses and calculations. Under the clear starlight night sky illumination, the spectral response characterization of the APD with green vegetation, concrete, and dark green paint is studied. The spectral matching factors are 0.4972, 0.5021 and 0.4979, respectively. The utilization rate of the infrared radiation highly increases in the night sky. These results can be used to provide the theoretical basis for the night vision system construction based on APD.