To understand the laws of trajectory stability for natural supercavitating vehicle in the condition of changing cavitation number,the simplified equations were derived and the corresponding simulation software for trajectory were developed,by which the trajectory characteristics of natural supercavitating vehicles were obtained at the speed of 110 m/s.The theoretical prediction results show that the balance of forces was broken by the influences of the changing cavitation number,and the periodically oscillation around the cavity wall was happened by the interaction between the forces and attitude.