Abstract:The dissociation of natural gas hydrate will generate a large amount of gas and water. In the case of poor permeability of the soil layer, a large amount of gas cannot escape in time, and the pressure is not easily transmitted to the outside, so that the excess pore water pressure in the soil layer increases rapidly and the effective stress decreases. At the same time, the cementation between hydrate and sediment is greatly reduced after hydrate dissociation. As a result, the sediment strength will decrease and large-scale deformation or instability will occur, which will lead to seabed instability and other disasters. Based on the basic theory of thermodynamics, an excess pore water pressure model considering the partial dissolution of methane gas produced by hydrate dissociation was established, and then its influencing factors were discussed in this paper. Finally, the influence of hydrate dissociation on the stability of seabed was studied in allusion to the condition of the South China Sea. The results show that the excess pore water pressure generated by hydrate dissociation first increases rapidly, then increases slowly, and finally tends to be stable; the initial saturation, plasticity index, water depth, burial depth of sediments, internal friction angle, etc. are key factors that influence the excess pore water pressure caused by hydrate dissociation; the key unfavorable factor that affects the stability of the seabed is the accumulation of excess pore water pressure rather than the weakening of strength of soil mass; the secondary dissolution of the methane gas generated reduces the excess pore water pressure, which alleviates the sliding of the slope to some extent.