The invention relates to mullite-carborundum microporous aggregates and a preparation method thereof. The technical scheme of the invention is as follows: the method comprises the steps: firstly, adding a pore former, which is 0.5wt% to 5.0wt% that of raw materials, into 45wt% to 70wt% of alumina raw material and 30wt% to 55wt% of crystalline silicon cutting waste liquid which serve as the raw materials, carrying out uniform mixing, carrying out compression molding at the pressure of 20MPa to 50MPa, carrying out natural drying, and carrying out baking for 12 to 24 hours at the temperature of 60 DEG C to 110 DEG C; then, heating the baked product to the temperature of 1,350 DEG C to 1,550 DEG C, carrying out heat preservation for 1 to 12 hours, then, naturally cooling the baked product to room temperature, and carrying out crushing, thereby preparing the mullite-carborundum microporous aggregates. The crystalline silicon cutting waste liquid contains the chemical ingredients, i.e., SiC, Si and C, wherein the content of SiC is not lower than 35wt%, the content of Si is not lower than 15wt%, and the content of C is not lower than 4wt%; the content of Al2O3 in the alumina raw material is not lower than 60wt%; the grain size of the alumina raw material is smaller than 0.074mm. The mullite-carborundum microporous aggregates and the preparation method thereof have the characteristics of low production cost, simple process, resource saving and environment protection; the prepared mullite-carborundum microporous aggregates are small in coefficient of thermal conductivity, high in strength, good in wear resistance and high in erosion capability.