Abstract: Single-photon detectors and time-correlated single-photon counting techniques have been widely used in pulse laser ranging system and three-dimensional imaging systems. Analyzing the factors influencing detection precision will improve the performance of ranging system. In this paper, a theoretical model of single photon ranging system based on TCSPC was established and the main factors affecting the accuracy was analyzed. The main factors included laser pulse intensity and pulse width of echo signal statistics waveform and the latter depended on laser pulse width and time jitter of detector. And simulation of the detection process by Monte Carlo method was used to get the specific influence of the above factors on measurement accuracy. Finally, an experimental single photon ranging system is built in lab. The system has an accuracy of 4 mm about the target 10 m away by experiment and the accuracy verifies the simulation results under the same parameters.