Aiming at the characteristics of the long tubular powder, a one?dimensional discrete group gas?solid two-phase flow model was established for the large caliber high speed Davis gun with a tubular modular charge. In this model, the tubular modules were described by the Lagrangian system without being assumed as pseudo?fluid, whereas the gas field is described by Eulerian system. The new model was used to simulate a 480 mm Davis gun. The simulation results were compared with test results, and the model was verified to be feasibility. This study provides a new method to research the interior ballistic performance of Davis guns.