Pseudo-random bitstream ranging model is researched and a new output signal to noise ratio (SNR) model based on photon statistics model is proposed. The relationship between SNR and code pattern of pseudo-random bitstream with different dead time is studied by Monte-Carlo simulation. The theory model is almost consistent with Monte-Carlo simulation. The results show that with the fraction of randomly distributed 1-bits in transmitted pattern increased, the system SNR is getting better firstly and then getting worse. Best pattern of transmitted bitstream according to different dead time may lead to the best SNR. According to new output SNR model, lower dead time brings better SNR. The system SNR increases firstly then gets down with the growing signal photon counting. Gaussian distribution timing jitter is introduced to reconstruct received bitstream pattern formed from the arrival times of returning single photon. It is found that higher rate of bitstream brings higher possibility error of single time value. Suitable bits rate is restricted to 1 GHz to reduce the probability of ranging error.