A 1550 nm fiber laser ranging experiment system combining pseudorandom modulation technique and single photon counting method is developed. In order to overcome the low detection rate problems of ordinary InGaAs single photon detectors due to restraining after pulses, a discrete amplification photo detector is used as the single photon detector with a counting rate of 100 MHz in this system. A sensitivity of -83.6 dBm is achieved under room temperature with the detector’s biasing voltage of 53 V and the pseudorandom serial length of 81.91 μs. The system performance is tested under different signal powers and pseudorandom serial lengths. A range accuracy of 12.7 cm is obtained with -78.6 dBm signal average power and 163.83 μs pseudorandom serial length. The system parameters of a spaceborne laser altimeter with this technique are proposed according to the experimental results.