Abstract: Hydrodynamic parameters are important parameters for the maneuverability design of the underwater vehicles. The finite element analysis is conducted on the hydrodynamic performance of a flap rudder used in an underwater vehicle under different operating conditions by using the computational fluid dynamics (CFD), and the lift and drag characteristics parameters of the flap rudder are obtained. By comparing and analyzing these parameters, the optimal efficiency angle and maximum lift angle of the flap rudder under different operating conditions are obtained. It provides important reference basis for the optimal control strategy of the flap rudder for subsequent underwater vehicles.