Abstract: Steel slag mud is a byproduct generated after the wet ball milling and magnetic separation of BOF slag, whose hydraulic cementitious property is relatively poor. The physical and chemical activation technologies of steel slag mud were introduced. The experimental results show that physical activation can significantly improve the mud activity. The stimulating agent, such as gypsum and its related products, shows good chemical activation effect on the mud. When mixed with 4% plaster of Paris or 5% natural gypsum, the activity of mud powder can meet the national standard for the first-class micro-powder. Complementarities exist between the mud powder and the slag powder, both of which can be mixed in proper proportions to produce steel slag cement. The slag powder favors the increase of mechanical properties while the mud powder improves the volume stability of steel slag cement.