The invention provides a method for improving the grinding characteristic and activity of stainless steel refining slag. The stainless steel refining slag, calcium carbonate and potassium tetraborate are mixed according to a certain proportion and put into a grinding machine to be ground for 120-150 min, then slaked slime and sodium metasilicate nonahydrate of a certain proportion are added, and then the mixture are ground for 30-60 min; and the mixture comprises, by weight, 94-96% of the stainless steel refining slag, 0.5-3% of the sodium metasilicate nonahydrate, 0.5-1.5% of the calcium carbonate, 1-2% of the slaked slime and 0.1-0.5% of the potassium tetraborate. The ratio of the content of Na2O to the content of SiO2 in the sodium metasilicate nonahydrate is 1.00-1.06. According to the method, the physical and chemical combined mode is adopted, the grinding characteristic of the stainless steel refining slag is improved, the production cost is reduced, the utilization efficiency of the stainless steel refining slag is improved, the activity of the stainless steel refining slag can be further triggered on the basis that the fineness is increased, and a positive effect is achieved for resource utilization of the stainless steel refining slag and ecological environment protection. The method is simple in technique, low in price and easy to apply and popularize and has remarkable economic and social benefits.