Abstract: Interior trajectory terminal is a transition from interior trajectory to middle trajectory, and it′s parameter is important to the safety of mine launching via platform. A mine obtains its muzzle velocity through the work of high pressure gas in interior trajectory, and keeps moving forward only with inertia in interior trajectory terminal stage with the restriction from submarine torpedo tube. Based on the force analysis of mine motion in interior trajectory terminal, a dynamic model of interior trajectory terminal is established by using the second Lagrange formulation. A hydrodynamic force is added to determine the generalized force in the right side of the formulation. Some figures of interior trajectory terminal parameter versus initial velocity of mine are achieved. Simulation result shows that appropriate increase of initial speed of mine can improve the safety of mine launching via platform.