In order to achieve high sensitivity space laser communication and improve the anti-interference ability of the transmission channel， this article combines single photon detection technology and pulse position modulation technology， the single photon detector avalanche is quenched by the combination of the gated circuit and the feedback quenching circuit. The insert frame header method was designed to modulate and demodulate the pulse position. The pulse position modulation and demodulation process was simulated by field programmable gate array， which verified the effectiveness and feasibility of the insert frame header method. On this basis， a 1 550 nm pulse position modulation laser communication experiment was built， and the performance of the single photon detector under different parameter was tested at the same time. The results show that the single photon detector has the best performance when the detection efficiency is 25%， the trigger delay is 8.00 ns， the gate width is 5.0 ns and the death time is 0.1 μs. Finally， the detection sensitivity of single photon detectors with different modulation rates was tested. The results show that the communication sensitivity is -51.8 dBm when the communication code rate is 1 Mbps； the communication sensitivity is -41.0 dBm when the communication code rate is 4 Mbps， which realizes high sensitivity space laser communication.