Abstract: For the crustal stability assessment of cross-sea channel of the Qiongzhou Strait, the Sonar Beam S-150d scan sonar system was applied to the topography investigation of the seabed in Qiongzhou Strait, in which the side scan sonar image of the engineering region was obtained. Through data analysis and image interpretation, the types of geological hazards and their potential harm were analyzed. Microgeomorphic units including soft ground, movable sand wave, bank slope and active tectonics are found on the Qiongzhou Strait seabed, which will cause relative geological disasters in the construction and operation stage of cross-sea channel engineering. All the data and analysis provide basic information for the crustal stability assessment of cross-sea channel engineering and technical support for the optimization of engineering planning and implementation. It shows that the side scan sonar technique can be applied to the investigation and assessment of the stability of the submarine crust.