Abstract: According to the requirement of stable operation of conical-grain solid rocket motor (conical-grain SRM) under lateral overload, a calculation model of internal ballistic performance of the conical-grain SRM was established by combining with mature overload burning rate model and burning surface regression model. The differences of the conical-grain SRM performance parameters under different lateral overload conditions were compared and analyzed by means of the simulation calculation. At the same time, the overall performance parameters of the conical-grain SRM under typical overload conditions were obtained, and the influence mechanism of lateral overload on the conical-grain SRM performance was preliminarily revealed. The results indicate that under later overload, the burning surface of conical-grain SRM becomes concave, accompanied by an increase in both burning surface area and mass flow rate. Under sustained overload conditions, the variation curves of burning surface area and mass flow rate exhibit a double-peak characteristic. Furthermore, the lateral overload advances the pressure peak and shortens the burning time. Changes in the direction of lateral overload result in a reduction in burning time, and when lateral overload G=100g, the burning time was shortened by 0.25 s due to the change in the direction of lateral overload. Even under a sustained 100g lateral overload, the change rates of the average thrust during the burning phase, total impulse, and specific impulse all remain below 10% compared to the condition with no overload.