The traditional way to underwater thrust vectoring is mainly based on a specially designed mechanical system which provides the propulsion system additional degree of freedom. This method is effective in field applications. However, there are several drawbacks such as complex structure and large dead weight. In this paper, a new type of thrust vectoring method, based on inflated surface is proposed. There are six inflatable surfaces uniformly distributed around the axis of the propulsor. The mechanism of this method is the Coanda effect. Through the control of the curvature of the surface, the deflection angle can be adjusted. The effect of the depth, the size and the curvature of the surface on the deflection angle is numerically studied. The deflection angle decreases with the depth, but increases with the surface size. The deflection angle first increases then decreases with the curvature due to flow separation. A maximum deflection angle of 14 degrees is realised. The pressure and velocity distribution is given to illustrate the mechanism behind the variation of deflection angle in different cases.