High frequency underwater laser measurement system can achieve high precision detection of small underwater targets,which is the basis for mapping seabed topography and obstacle avoidance for unmanned underwater vehicles.In order to achieve high precision detection of weak targets such as underwater fishing nets and triangular cones,a small size,high precision,high frequency heavy frequency underwater laser ranging software and hardware system is designed.By studying the real time signal responsiveness,spectral sensitivity and other important performance parameters of the APD,a high gain laser receiving hardware circuit based on the SAE500VSM photodetector is designed and implemented.Underwater laser ranging detection experiments at different distances are carried out,and the results show that the high frequency laser ranging system is able to effectively detect small targets in water with a detection accuracy of 15cm.