River dredging can improve the flood control，drainage and irrigation capacity of the river. However，due to construction disturbance，some dredging projects will cause stress adjustment，unloading deformation，and damage of the river bank slope，affecting the slope safety and project quality. Taking the river dredging project in Boluo county as an example，combined with the unsaturated fluid structure coupling theory，this paper analyzes the influence of dredging depth on bank slope sliding surface，safety factor，plastic failure and displacement of monitoring points. The results show that the larger the dredging depth is，the larger the landslide volume will be and the lower the safety factor of the slope will be. When the dredging depth is 1.6m，the safety factor is 1.58，which is 9.19% lower than the original bank slope；the depth of dredging has a significant impact on the plastic failure of the slope. When the excavation reaches the design height，the plastic deformation failure range of the slope angle is about 1/3 of the length of the free face；With the increase of excavation depth，the horizontal displacement of the four slope monitoring points shows an increasing trend，but the nonlinear characteristics are obvious，showing a logarithmic function growth；With the excavation until the final stage，the groundwater in the bank lift flows towards the dredging direction，and it flows most quickly at the outlet.