In order to study work process of three-dimensional dual-burning rate grain solid rocket motor, simulation was made based on UDF of FLUENT and compared with the results of experiment. The results show that there is a lag in the tube section in the flame propagation of ignition, comparing with the star section of the grain. We can carry out the shift of three-dimension dual-burning rate grain by integrating structured mesh with smoothing methods, dynamic layering and local emeshing approximately. However, a further investigation should be holding in the area of unstructured mesh and local emeshing. As a whole, the calculated results compare favorably with experimental data.