Abstract: To analyze the bank slope instability of channel reservoir during water stage falling after flood season, this paper considers the interaction of groundwater infiltration, hydrostatic pressure, pore water pressure, and other factors. The limit equilibrium method is used to examine the effects of the difference between riverside water level and groundwater level on bank slope stability, as well as the effects of water erosion and underground water level. The results show that a quicker river stage falling leads to a more unstable bank slope. Bank collapsing is also intensified by the lateral erosion or bed scour in the river or the lowering of groundwater level.