The physical and chemical properties of industrial waste slag used for preparing iron and steel slag powder in T Company were analyzed. In view of the problems existing in the closed-circuit grinding system of G95 steel slag powder pilot production stage, the effective length of each bin of tube mill and the parameters of screen separation bin plate were adjusted, and the grinding body grading of the second and third bins were optimized. After the technical improvement, the grinding capacity of the system is significantly improved. The specific surface area of steel slag powder is increased from 168m2 / kg to 296m2 / kg, and the system output is increased from 35.6t/h to 44.4t/h. The output of iron and steel slag powder can be increased by about 210t each day. Calculated based on the cost of steel slag powder is 100 CNY / t, the economic benefit can be increased by 630,000 CNY per month.