The solid fuel ramjet is related to the missile flight conditions through the inlet. Compared with other kinds of ramjet, the marked characteristic of the solid fuel ramjet is that its propellant combustion chamber process is not only concerned with the propellant composition, motor structure and combustion pressure, but also dependent on the air parameter in the combustion air inlet. Hence, the operation process is rather complex. The operation process simulation model, the first of its kind in China, was established, and the effect of the missile flight mach number and height on the motor performance was discussed.