The dissociation of gas hydrates can increase pore pressures greatly, thereby causing the shallow layers of submarine slopes to fail. Given the high failure risk of shallow subsea soils, it is important to understand the stratum response mechanisms after hydrate dissociation. In this paper, submarine slope failure triggered by overpressure fluid associated with gas hydrate dissociation is investigated in laboratory experiments. A two-layer geological model is built based on actual geological data, and pressurised air is injected into the model to simulate the overpressure fluid. The pore pressures, surface displacements and internal deformations of soils are measured and compared under different conditions, and their evolution processes are analysed for various parameter values. The results show that the accumulation of pore pressure increases with the thickness of the soil layer and leads to layered fractures. The failure pattern can be generalised into two types: (a) disc-shaped failure and (b) penetration failure. In disc-shaped failure, a major failure occurs when the shear stress reaches the shear strength, whereas tensile fracturing is a major effect in penetration failure. This achievement is very important for a deep understanding of submarine landslides induced by overpressure fluid, as well as for risk assessments of ocean engineering sites.