Abstract: On the purpose of improving the utilization level of mine solid wastes and reducing the cost of backfill mining, this article reports an experimental study on preparing cementitious materials for backfilling by using water-granulated nickel slag. Mechanical and chemical activation methods were adopted to improve the cementitious activity of the slag. Taking the strength of backfill bodies as evaluation standards, the hydration activity and cementitious performance of the slag were investigated by changing the grinding fineness and activated agents, and the chemical activation mechanism was analyzed. The results indicate that the cementing agent prepared from the slag (occupying 85% of the total raw materials) can be used to replace cement and meet the production requirements of back-filling materials.