In order to reasonably evaluate the primary gas/air mixing combustion process in the secondary combustion chamber of solid rocket ramjet, an evaluation method of mixing combustion process of solid rocket ramjet based on particle mass concentration was proposed. Numerical simulation method of engine was established and verified by ground test. Aiming at the mixing combustion process in the afterburner under different working conditions, the changing trend of mixing degree and combustion efficiency in different definitions was compared by numerical simulation. Results show that the proposed particle mixing degree and particle combustion efficiency shows the greatest correlation, and the average maximum information coefficient reaches 0.916 3 under different working conditions. Moreover, the primary gas/air mixing and combustion process shows the following correlation laws:the particle combustion efficiency increases with the increase of particle mixing degree, and when the particle mixing degree exceeds a certain threshold, the particle combustion efficiency remains relatively stable. And the law is verified by experiments.