For large bending moments in the monolithic lock chamber floor，this paper studies the influence of setting a relieving slab on the lock wall on the internal force of the lock floor.The paper adopts three-dimensional nonlinear finite element analysis and draws the following conclusions：1) Setting a relieving slab on the lock wall will reduce the compressive stress on the upper surface and tensile stress on the lower surface of the side pier floor.In addition，it will increase the tensile stress on the upper surface at the mid-span and the settlement at the side pier floor.2) Compared to the relative height，the cantilever length of the relieving slab will have a greater influence on the lock floor bending moments.3) During engineering design，the relieving slab is set at a height of 1/3-1/2 of the lock chamber wall and below the water level of the drainage pipe.In this condition，the stress condition of the lock floor is good with the cantilever length of the relieving slab set at 0.10-0.15 times the lock chamber wall height.The lock chamber floor designed with the relieving slab has better stress conditions，providing references for the height to width ratio and foundation soil quality of similar projects.