In order to reasonably set the bias voltage of an avalanche photodiode (APD) detector and thus to achieve the adjustable multiplier factor at a constant temperature, we analyse the working principle of the APD detector and factors of influencing its detection sensitivity, and measure the detection sensitivity of the APD detector in laboratory. The experimental results show that the APD detection sensitivity ranges from -47 dBm to -34 dBm when the communication rate changes from 10 Mb·s-1 to 2000 Mb·s-1. When the bias voltage changes from 55.0 V to 70.0 V, the detection sensitivities at communication rates of 10,100,1000 Mb·s-1 increase by 5.7,6.5,7.8 dB, respectively. The experimental results well validate the theoretical analysis, which provides technical support for improving the receptivity of space laser communication system.