Abstract: With the rapid development of admixture concrete technologies and increasing requirements of building for energy saving, the experimental studies on the influence of the fineness and addition of the granite powder on concrete microscopic pore structure with MIP (mercury-intrusion porosimetry) method are carried out in order to prove the feasibility of the granite powder as concrete admixture at the micro level and reveal the impermeability and antifreezing properties of concrete at the micro level. It is found from the studies that the smaller the fineness, the better the filling effect on smaller pores, but the integrated filling effects perform poorly; when the addition is 10% and 20%, the granite powder fineness is 0~150 μm, which plays an optimized role in concrete porosity and pore structure parameters; when the admixture dosage is controlled within 30%, the granite powder fineness is 0~ 150 μm, which is in favor of improving the impermeability of concrete; when the granite powder dosage is controlled within 20%, it can ensure the antifreezing properties of admixture concrete and non-doped powder concrete at the same level; and the admixture concrete antifreezing level decreases with the addition of granite powder being up to 30%.