Abstract: According to the stable operation requirement of conical-grain solid rocket motor (SRM) under lateral overload, a internal ballistic performance calculation model of the conical-grain SRM was established by integrating well-validated 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 simulation calculation. At the same time, the comprehensive performance parameters of the conical-grain SRM under representative overload conditions were obtained, and the influence mechanism of lateral overload on the conical-grain SRM performance was preliminarily revealed. The results indicate that lateral overload inducecs concave deformation on the burning surface of conical-grain SRM, alongside simultaneous rises in both burning surface area and mass flow rate. Under the sustained overload conditions, the evolution profiles of burning surface area and mass flow rate present a distinct double-peak feature. Furthermore, the lateral overload shifts the pressure peak forward and reduces total burn duration. Reorienting lateral overload vector further shortens the burning time, and when lateral overload G=100g, the burning time is shortened by 0.25 s due to reversing lateral overload direction. When subjected to a sustained 100g lateral overload, the relative variation rates of the average thrust, total impulse, and specific impulse during the burning phase all remain below 10% compared to the non-overload case.