A new method to measure transfer time delay in optic fiber more accurately is proposed to deal with timing jitter of single photon avalanche detector worked in Geiger mode. The arrival time of echo optical signal is determinated by adjusting the arrival time and width of gate signal to make the photon count rate reach the maxim value. The method avoids the intrinsic timing jitter of single photon avalanche detector. After deliberately theory analysis, system experiment is performed in fiber of length approximate 125 km, the experiment shows that measurement precision is about 35 ps and the accuracy is about 13 ps.