Aiming at the problem that the semi-autogenous grinding mill of a copper?nickel ore in Xinjiang is seriously accumulated and the fineness of the grinding products is not up to standard, based on the determination of the mechanical properties of the ore, the fineness comparison of the semi-autogenous grinding mill grinding products was studied. In the method, the steel ball medium ratio was taken as a single variable, and the comparison test of the grinding index was carried out. The discrete element method was used to verify the laboratory test conclusions. In the end, the optimal medium ratio scheme of the semi-autogenous grinding mill was determined as follows: ?150:?120=1:2. The results showed that the average specific weight was 3.36 g/cm3, the average hardness coefficient was 7.93, the average static elastic modulus was 3.11×104 MPa, the average poisson′s ratio was 0.26, the ore was moderately hard as well as the ore with brittleness and toughness existed. Under the same grinding cycle conditions, the yield of 25~80 mm fraction of the hard stone grade gradually reduced in the recommended scheme of the semi-autogenous grinding mill. The plant scheme was reversed. After the three grinding cycles, the yield of 25~80 mm fraction of hard stone in recommended scheme was 4.19 percentage points lower than that in the plant scheme. The yield of three size fraction of +100, ?2.5 and ?0.074 mm were 0.25, 13.79 and 4.80 percentage points higher than that in the plant scheme respectively. Compared with the larger scheme, the recommended scheme showed better grinding ability as well. Under the same number of grinding cycles, the yield of 25~80 mm fraction of recommended scheme reduced by 3.36 percentage points, and the fineness of ?0.074 mm increased by 2.24 percentage points. The sum of the normal energy utilization of the recommended 25~80 mm fraction was 56.19%, which was 1.82 and 2.30 percentage points higher than the plant scheme and the larger scheme respectively. The recommended scheme showed better hard stone crushing ability. The results of the simulation tests were consistent with the laboratory test results. Based on the comparison of the test results, the recommended scheme had obvious advantages. Ensuring the fineness of the grinding products was in a good level, the accumulation of hard stones was fully solved, which provided a method to learn for a similar problem for related factories and mines.