In order to solve the calculation of actuator ejection mass in pyrotechnic folding rudder, this paper investigates the calculation method for equivalent ejection mass of variable thrust in the Internal ballistic equations of pyrotechnic folding rudder, and obtains the fitting curves of equivalent ejection mass and gunpowder thrust in the case of variable forces and calculates the gunpowder thrust curves during the unfolding process by establishing the dynamic simulation model of the pyrotechnic folding rudder. After test verification, the test results are consistent withe the simulation results, indicating that the method is accurate and effective, and provides a theoretical basis for the design of the pyrotechnic folding rudder.