Abstract: during the long-term operation of hydropower station, the defects of dam concrete face slab in different degrees will directly affect the safe operation of hydropower station. The existing detection methods for the above water part of the dam are relatively rich, while the detection methods for the underwater part are relatively simple. In this paper, the underwater side scan sonar scanning survey and the underwater robot detection are combined to detect the underwater part of the dam panel of a hydropower station in Guizhou. The test results show that the underwater side scan sonar can evaluate the overall situation of the dam panel, and the underwater robot equipped with imaging equipment can obtain more refined dam panel data. The way of side scan sonar and underwater robot camera can provide technical guidance for the treatment of the apparent defects of the dam and improve the safety factor of the dam.