Abstract: The instability of the bank slope of the reservoir will cause great loss to the life and property of the people in the reservoir area. The landslide of the reservoir occurs in the periods of rapid falling and rising water level. The mechanism of slope landslide in the rising stage of water level is studied from the perspective of soil disintegration in water. A series of experiments on the disintegration of prisms and cylinders with the same volume and different bottom side lengths (diameters) are carried out. The disintegration tests on four kinds of cylinder samples with different sand contents in water are conducted. The results show that the larger the specific surface area of the same shape sample is, the faster the disintegration speed is. The deeper the water depth is, the shorter the disintegration time is. With the increase of the sand content, the disintegration rate of the soil sample is faster and faster. The larger the sand content of soil slope is, the more likely it is to be unstable.