To investigate the influence of the loading density of main propellant charge on the propagation characteristics of ignition charge gas in the granular propellant bed， the test platform for ignition and propagation of a large-diameter dense propellant bed was established， and the flame sequence diagram and the pressure changes of partial pressure gauges were recorded in tests. The porous medium model was used to simulate the granular propellant bed in the charge chamber， and the ignition and propagation model corresponding to the test device was established to numerically simulate the flow process of ignition charge gas in the granular propellant bed. The simulation results were compared with the test results to verify the reliability of the model， and then the propagation characteristics of temperature and pressure fields of gas in the propellant bed with different loading densities were calculated. The results show that the calculated results are in good agreement with the experimental flame propagation sequence process and the experimental pressure histories， which verifies the reliability of the model. Under the condition of any porosity， the axial displacement of flame front develops rapidly and the axial velocity decreases from 25-30 m·s^-1 to 10 m·s^-1 during 0-10 ms， ， and the axial velocity decreases to 2-3 m·s^-1 during 10-40 ms. Similarly， under the condition of any porosity， the development of radial displacement of flame front is concentrated during 2.2-3 ms， and the radial velocity decreases to 20-22 m·s^-1 at 3 ms. However， the radial velocity at the initial time is large for large porosity. When the porosity increases from 0.3 to 0.5， the pressure difference at different positions in the chamber decreases 16.7% from 0.24 MPa to 0.20 MPa， and the uniformity and instantaneity of ignition are improved. With the increase of porosity， the axial and radial resistances of the flame front in propagation process decrease， the axial expansion displacement of the flame front and the initial velocity of flame propagation in the axial and radial directions increase， but the final velocity tends to be the same. The smaller the pressure in the chamber， the smaller the pressure difference in the chamber.