Abstract: There are numerous mineral resources on the seafloor,and its prospect is broad. Compared with land mining,seabed mining is more threatened by overlying water bodies. In order to ensure the safe and economic operation of subsea mining projects,it is of great significance to find out the characteristics of the deformation,movement and destruction of the surrounding rocks in the mined-out area,and to determine the critical thickness of the waterproof pillars left at the top of the mining area. In this paper,the San-shan-dao Gold Mine Xinli Mining Area is selected as the research subject. A geo-mechanical experiment is carried out to reproduce the process of undersea filling mining and clarify the deformation and failure process characteristics of overlying strata. The test results show that the critical mining height of Xinli mining area is - 85 m,and the critical thickness of the reserved isolation pillar at the top is 50 m. When the critical value is exceeded,the goaf and the top aquifer suffer through failure,and the instability mode is fault activation. The research results can provide a theoretical basis for the selection of reserved pillar height in Xinli mining area,and also provide a reference for the mining safety of mines under similar geological conditions.