Signal-to-noise ratio (SNR) of lidar system affects directly the quality of the range image and intensity image. Using the theory of signal correlation detection, SNR of non-scanning lidar system is analysed under multi-pulse-accumulation condition. Simulation and analysis of SNR are conducted under considering APD arrays, work environment factors, lidar system parameters. SNR is improved by 9.35 dB under 100 pulses accumulation, and the sequential improvement is not obvious with increase of pulse accumulation. It is shown that SNR of lidar system can be improved by using pulse-accumulation method.