In a laser range finding system of a high maneuvering target reconnaissance system, when background changes randomly, the operation distance of the system is as far as a few dozens of kilometer. According to background noise, the operation state is adjusted adaptively to achieve higher sensitivity and signal noise ratio (SNR). According to the background noise and multiplication characteristics of the avalanche photo diode (APD) detector, the adaptive bias control method is researched. Based on constant false alarm rate control method, the laser range finding receiving front-end circuit is designed. The circuit gain and avalanche multiplication factors are controlled by time programmable gain (TPG) and time programmable bias (TPB) signals respectively. The adaptive characteristics are tested under static closed loop state. The dynamic closed loop state in field experiment is tested. The experiment of long-distance target detecting is completed through the experimental devices.