In order to explore the characteristics of ignition and flame-propagation process of the modular charge， a small metal modular cartridge was designed and the ignition test was carried out. On this basis， the internal ballistic two-dimensional gas-solid two-phase flow model of the test was established， the model was solved by using CE/SE method. The variation characteristics of flow field parameters in the chamber are obtained， and the numerical results are in good agreement with the experimental results. The numerical results reveal the changing process of the pressure distribution of the ignition tube and main charge area during the flame-propagation process， the flow law of the gas phase and the influence of its radial propagation effect on the combustion of the propellant in main charge area； The rupture of the cartridge’s end cap will lead to the formation of a shock wave in free space of the chamber， the reason for the formation of the shock wave are discussed. In addition， the numerical simulation of the gas jet of the vent hole breaking-progress under the hypothetical working condition is carried out， the gas phase flow law and the pressure-boosting law of the main charge area are studied. The comprehensive results show that under the condition of modular charge， the radial effect of the gas phase in the ignition tube is obvious during the entire ignition and flame-propagation process， and the particularity of the charge structure can easily lead to the formation of shock waves.