Abstract: For proper grain selection for the combustor and better design of the grain parameters, the grain for a thermal power torpedo combustor is taken as an example to establish the burning equations of the grain. And on the basis of the simulation and the performance confirmatory test, the influences of the grain parameters on the combustor interior trajectory are obtained. The results show that: 1) of all parameters of ignition grain, burning rate pressure exponent imposes the most significant influences on the peak time and peak pressure; 2) of all parameters of main grain, burning rate pressure exponent imposes the most significant influences on the peak pressure, the stable internal pressure in combustor and the burning time, and initial outside radius of main grain exerts the most significant influence on the peak time. Tests verify the effectiveness of the proposed model and the relevant results. This model satisfies the requirements of engineering practice. It may provide a theoretical reference for design and optimization of the grain, and provide a technical support to prediction of combustor interior trajectory.