Abstract: In order to reduce the loss of fine grain hematite in the process of the high intensity magnetic separation of the sijiaying iron mine, through the replacement of magnetic matrices in industrial test, the author proves that the optimized 1.5mm and 2mm mixed magnetic matrices is better for the separating effect of micro fine difficult selection hematite ore. The reason of the change of the sorting effect after replacing the magnetic matrices were analyzed theoretically. After industrial test the recovery increased by 10% and the metal recovery rate has increased by 1.3% for raw ore. The-325 mesh fraction in tailings decreased by an average of 5% and with an increase of 23.81 million per year for the company. The results have the value of industrial promotion and application.