Abstract: Modified steel slag was prepared by mixing molten fly ash and steel slag at high temperature. We have studied its microscopic structure and macroscopic mechanical properties.The results showed that: The content of the fCaO was decreased by adding modified steel slag; The strength of the modified steel slag cement is a little lower than the ordinary one, but the strength was still meeting the need of P·SS32.5R cement. It is feasible that modified steel slag can become one of the cement materials.