Abstract: The rapid fluctuation of water level of reservoir is liable to cause accumulation landslide, and the failure of reservoir slope often causes damage to hydraulic structures and reduces storage capacity. So that, study its mechanism and the deformation failure mode is important. The test was performed in a rectangular box with the length of 100cm, the width of 60cm and the height of 60cm. A plastic board was set up in the test box, which was used to simulate the bedrock impervious to water. A sluice was developed to implement the simulation of the rapid drawdown of water level. About 20cm thick accumulation was filled on the plastic board. The sensors were buried in the accumulation and used for measuring earth pressure and pore water pressure during rapid fluctuation of water level. The deformation of slope was recorded during the test process by digital camera. The experimental results indicate that the tensile cracks initiate on the surface of accumulation, and a local failure of slope toe have happened in the raising of water level, as the water decreases shear strength of soil; in the process of water level drawdown, the accumulation slips along rock base, and the residual pore-water pressure is a major factor in landslide. The failure mode of reservoir slope is pull-type, due to the landslide is triggered by seepage force.