Numerical simulation with discrete phase model was made on supersonic combustor with a strut-cavity structure to study the mixture characteristics of the supersonic combustor. The effect of the cavity's length to depth ratio (L/D) and the aft angle on the kerosene mixture characteristics was analyzed. The results show that the structure with big L/D contributes to the mixture of the fuel and air with higher mixture efficiency; the cavity with 30° aft angle involves more fuel than that with 45° aft angle, increasing the mass exchange between the fuel and the air in the cavity.