For the mechanics analysis of the underwater vehicle with damping plate, analyze the plate mechanics without wall and wall in unbounded flow field. Firstly, establish the expression of the force and moment of the damper on the whole body. Secondly, through the simulation, analyze the flow field around the damping plate, it is concluded that the moment of the fluid subjected to the damping plate does not show a simple linear relationship with the opening time. At last, the numerical simulation of the underwater vehicle with damping plate and without damping plate is carried out by using FLUENT software. The results show that the axial additional mass of underwater vehicle and reduces its tail flow rate. The above work provides a way for the damping plate to analyze the mechanical effects of the underwater vehicle.