Abstract: The gas balance equations were established for closed cavity based on the law of gas leak. The development of cavity was analyzed by the independence principle of the cavity expansion of Logvinovich and the cavity pressure is a function of time. The dynamic equations for vehicle gesture calculation were given and the load characteristics of the water entry and vehicle movement with supercavitation were analyzed. Considering the coupling of gas balance equations, cavity section expression and dynamic equations, the numerical method for calculating the unsteady process of water entry of a high-speed vehicle with supercavitation was obtain. The results show that whether considering the cavity elasticity or not makes big difference. Considering the cavity elasticity, the wall-wave phenomena can be simulated and the wave number is consistent with the engineeringly estimated one.