In view of the detection difficulties of caisson joints of the gravity wharf,underwater robot,multi-beam and 3D sonar scanning technology are used to detect.Test data shows that the effect of the underwater robot is intuitive and accurate;the multi-beam system has certain recognition ability for caisson joints,but has poor resolution for the smaller-width and longer-distance joints;the scanning of 3D scanning sonar detection is highly accurate,but the scanning range is small and the scanning efficiency is low.Based on the principle of testing,we analyze the reasons of the advantages and disadvantages of various methods and designs the 3D sonar measurement bracket independently according to the testing requirements,realize the measurement of any depth of the caisson joints,and obtain a good test effect.It may serve as reference for selection of the detection method of caisson joints.