In order to accurately calculate the parameters of the two-phase flow dynamics in the artillery and the movement law of the projectile in the bore, a simulation method for coupling calculation of the two-phase flow dynamics in interior ballistics and launch dynamics is proposed. The variation law of the interior ballistics parameters obtained by the classic interior ballistics, the two-phase flow in interior ballistics without considering recoil motion and the coupling calculation are analyzed. The bore pressure and initial velocity obtained by the coupling calculation are in good agreement with the experimental values. The motion law of projectiles obtained by basing on the classical interior ballistic theory and the coupling algorithm are analyzed, the coupling algorithm can obtain the results reflecting the actual motion change law of the projectiles in the bore. It shows that this method can provide a reference for accurate calculation of interior ballistics and launch dynamics.