Abstract: The natural cavity around a submarine-launched vehicle and the deviation of its axis under maneuver conditions were investigated based on the principle of cavity expansion independence. The theory of slender bodies was used to calculate the hydrodynamic force on partially wetted regions. Then a mathematical model for the underwater motion of a submarine-launched vehicle was developed for the longitudinal plane. The underwater motion under cavitation conditions was analyzed by numerical simulation. The numerical results show a good agreement with experimental results. The results show that submarine speed will induce trajectory divergence, which is disadvantageous to attitude stability. However, the additional radial force due to cavitation can correct the attitude to a certain degree.