Abstract: In a cruise phase, a supercavitating vehicle is enveloped almost completely by a cavity, the interaction between the cavity wall and the tail of the body generates a planing force which changes rapidly, and this force is the main factor that causes the unstability of the bodies. Because of the complexity of interaction mechanism, it is nearly impossible for one to work out the planing force expression without model differences or parameter uncertainty. In order to solve this problem, this paper applies a series of transformation, so that the system model is expressed as a form of feedback connections which contains linear parts and nonlinear parts, then a sufficient condition for the absolute stability of the system is given, based on a circle criterion theorem. According to the condition, a state feedback pole assignment method is adopted to design the controller. The simulation results show that for different nonlinear characters, like model uncertainty and parameter uncertainty of a planing force, the system with this controller can get absolute stability through the rational allocation of closed-loop poles.