The slope safety and stability is very important to the construction safety and operation safety of hydropower station, and the rise and fall of water level in reservoir has an important influence on the stability of bank slope. Especially in the alpine and canyon areas of Tibet, the problem of bank slope security and stability formed by ice water accumulations is more prominent. Therefore, the three-dimensional finite element analysis method and strength reduction method are used to analyse the stress distribution and stability of the ice water accumulations slope of a hydropower station in Tibet under natural state, normal water level and normal water level + seismic conditions. The results show that the reservoir impounding has great influence on the stress disturbance of the slope. The stability of the slope is poor under the two conditions of normal water level and normal water level + seismic conditions. To ensure the safety and stability of the slope, it is suggested to remove the surface covering layer, increase the strong support and reduce the excavation height. The results of this study can provide reference for similar slope engineering design and treatment.