In this paper, a mathematical model is built to determine the working parameters on the combustion chamber of a solid fuel rocket engine. Based on the theoretical basis established for this model, the parameters of the gas flow in the nozzle of the solid fuel rocket engine such as velocity, pressure, and temperature are determined by Matlab software. Selected C5K solid-fuel rocket engine for model verification. The results of the article are the theoretical basis for the process of calculating the nozzle design to ensure high accuracy.