When a high-speed cavitated weapon moves under water, the flow properties are important issues for the sake of the trajectory predication and control. In this paper, a single-fluid multiphase flow method coupled with a natural cavitation model is proposed to numerically simulate the free moving phase of an underwater supercavitated vehicle under the action of the external thrust. The influence of the cavitator’s deflection angle ranging fromo-3 to3o on the cavity pattern, the hydrodynamics and the underwater trajectory is investigated. Based on computational results, several conclusions are qualitatively drawn by an analysis. The deflection angle has very little effect on the cavity pattern. When the deflection angle increases, the variation curves of the vertical linear velocity, the lift coefficient and the pitching moment coefficient become flatter. In the phase of the second natural cavitation, at a same time, the greater the deflection angle is, the lower the drag and the lift coefficients will be and the higher the pitching moment coefficient becomes. At the finishing time of the free moving phase, when the deflection angle lies in the small range ofoo-1-1, the position of the center of mass and the pitching angle of the vehicle are more close to each other. However, when the deflection angle is less thano-1 or greater than1o, the position of the center of mass and the pitching angle change greatly. If a proper deflection angle of the cavitator is adopted, the underwater vehicle can navigate in a pseudo-fixed depth.