In order to prevent the ship cabin grounding accident of ship lift, a set of redundant water depth detection system based on ultrasonic scattering analysis is developed. Based on the scattering characteristics of obstacles encountered in underwater ultrasonic transmission, the system uses FPGA to control the ultrasonic transmitting array to build multiple transverse ultrasonic relative paths in the cabin of the ship lift, and collects the sound pressure data through the receiving array, and sends the data to the software for data analysis and calculation of the affluent distance. The system has been used in the chamber of Xiangjiaba ship lift. It has the advantages of strong stability, convenient installation and high real-time performance.