A floating ship draft system based on attitude compensation is designed which is focused on ensuring navigation safety and confirming the ship draft in the navigation test of Xiangjiaba Hydropower Plant ship lift. The system carries out the analysis of the ultrasonic underwater propagation characteristic and build the transmit model of the ultrasonic in lock chamber. According to the model of ultrasonic directivity, the system can find the amplitude matrices of the ultrasonic. Combine with the equipment attitude of obliquity sensors and the equipment depth of pressure sensors, the system can calculate the ship draft by building reference frame. The system proves its science and practicality by the field trial operation and expert interrogatory.