Based on the influence of composite cementitious materials on the hydration of Portland cement, recycled brick/concrete composite micro powder was used as supplementary cementitious material to replace cement, and mechanism of the effect of composite micro powder on the workability, mechanical properties, and microstructure of concrete under the substitution rate of 0%, 15%, 30%, 45% and the mass ratio of 8∶2and 6∶4 was studied. The results show that the fluidity decreases as the increase of brick powder ratio and composite micro powder substitution rate, but the fluidity changes less than 15%; at the beginning of hydration, the composite micro powder mainly plays the roll of filling. The 7d compressive strength of composite micro powder concrete is slightly lower than that of ordinary concrete. With the prolongation of hydrating age, the 28d compressive and splitting tensile strengths increased by 42% and 101% respectively at the substitution rate of 15% and the mass ratio of 6∶4 with composite micro powder.