Abstract: A single Φ150 mm steel ball media size in a semi−autogenous grinding ball mill in an iron ore plant in Panzhihua, Sichuan does not match the feed size and the mechanical properties of the ore, and the single steel ball size leads to high mill energy consumption and low efficiency.The maximum ball diameter of 150 mm was determined by using Bond Gong ball mill index test and Azzaroni formula, and the recommended steel ball grading of m(Ф150 mm)∶m(Ф120 mm)=1∶2 was verified to be the best by grinding test in a small mill with D×L 450×450 mm. The recommended steel ball gradation was finally confirmed to be the best. In this study, the results of laboratory grinding tests showed that the recommended steel ball grading reduced the stubborn yield by 0.32 percentage points and increased the yield of γ_-0.074 mm by 3.20 percentage points compared with the on-site steel ball grading; the results of discrete element (DEM) simulation experiments showed that the recommended steel ball grading increased the tangential collision energy utilization by 2.98 percentage points and the normal collision energy utilization by 1.90 percentage points compared with the on−site steel ball grading. The results of discrete element (DEM) simulation experiments show that the recommended ball gradation has improved the tangential collision energy utilization by 2.98 percentage points, the normal collision energy utilization by 1.90 percentage points, and the collision energy to the liner plate by 306.9 J. Thus, it is verified that multi−stage ball gradation can improve the energy utilization of semi−autogenous grinding ball mill.