Abstract: A novel research method for supercritical carbon dioxide phase transition ejection considering rigid-flexible coupling effects was proposed, successfully addressing the limitation of traditional interior ballistic models that ignore the rigid-flexible coupling effects between the flying vehicle and the vehicle-mounted launch system. The BWR equation of state was employed to describe the thermodynamic behavior of supercritical carbon dioxide, with analytical expressions for key thermodynamic parameters derived through the departure function method. A closed interior ballistic equation system was constructed and numerically solved using the fourth order Runge-Kutta method. A rigid-flexible coupling dynamic model was established, with the calculation results from the interior ballistic model applied as thrust loads to the system for simulation. Simulation results show that this method improves projectile exit attitude prediction accuracy compared to interior ballistics models and can make a launch system load analysis, providing theoretical support for vehicle-mounted mobile launch system design and optimization.