Air classifier mill (ACM) is widely used in powder coating and mineral comminution process. One of the problems typically presenting in ACM is over-grinding, which leads to high energy consumption and broad particle size distribution (PSD). To decrease the excessive amount of fine particles in the products, 6 configurations of grinding pins with ditches in the impact surface were used in the experiments. The width and depth of ditches varied from 1.35 mm and 1 mm to 4.75 mm and 3 mm, respectively, while the interior angles in the ditches are the same. The particle size and PSD show that the ditches on the grinding pins have significant effect on the D-10 values and the particle size span. The deepest and widest ditches (P4) result in largest D-10 and smallest span in this study. The Dios of products ground by P4 increase by 24.1% for fine powder (D-50 = 25 mu m) and 16.0% for coarse powder (D-50 = 33 mu m), while the span decreases by 6.9% (D-50 = 25 mu m) and 6.4% (D50 = 33 pm) compared to regular cylindrical pins (PC), respectively. Meanwhile, it is found that the P4 configuration improves the energy utilization efficiency by 7.6% (D-50 = 25 mu m) and 3.4% (D-50 = 33 mu m), compared to that of the original PC pins. (C) 2018 Published by Elsevier B.V.