Abstract: The dissociation of gas hydrate in seabed produces a lot of gas. If the seabed is permeable, the gas will escape, which will lead to the damage of the seabed, and to the decrease of the density of sea water and to threaten the safety of the structures above. In this paper, the movement and the expansion behavior of gas in the water are studied, then the damage of the seabed due to the gas escape is analyzed. The effects of gas pressure and thickness of soil layer are investigated. The expansion angle of gas in the water is obtained. The characteristics of the hole size induced by the gas escape under various gas pressure and soil thickness are also obtained. These results can be used in further research and practice.