Cold flow field and simple-reaction flow field of the combustion of HTPB and PS within the solid fuel ramjet (SFRJ) are simulated using PHOENICS program. The result shows that the reattachment point moves forward so that the flow field structure is altered in case of combustion. In case of cold flow, the reattachment point doesn't change with inlet temperature, but it does so in simple-reaction flow field. And it doesn't change with inlet mass flux in both conditions.