To investigate the distribution characteristics of propellant grains during ignition and flame-spreading of modular charge, a visualized modular charge experiment platform was designed. The test of Φ130 mm×100 mm single-modular charge ignition, rupture of the cartridge, and the movement of the propellant grains was conducted, and recorded by high speed camera system. A three-dimensional unsteady-state gas-solid two-phase flow model of the modular charge cartridge rupture and particle movement was established based on the gas phase-solid particle coupling method. Under different initial loading conditions of the cartridge, the distribution characteristics of propellant grains during the modular charge ignition and instantaneous process of flame spreading were analyzed. The simulation results indicate that, in the four simulated conditions that the distance between the initial loading position of modular cartridge and the primer is 40, 80, 120 mm and 150 mm, during the modular charging ignition and flame-spreading, the grains are finally distributed in the cartridge and the chamber on the right side of the modular cartridge. And they appear as a combination form horizontal and slope from primer side to pressure control diaphragm side. When the distance between the initial loading position of the modular charge and the primer is increased from 40 mm to 150 mm, the axial length of the horizontal stack is reduced from 269.5 mm to 200.4 mm, and the slope angle of the sloped stack is reduced from 25.03° to 21.31°. As the initial loading position of the module moves to the right, the axial length of the horizontal stack of grains becomes short, the stack thickness increases, and the slope angle of the sloping stack decreases.The numerical simulation results are basically consistent with the the sloping accumulation of the propellant grains observed experimentally, which verifies the rationality of the model.