Abstract: Objective To explore the feasibility, mechanical properties and hydration mechanism of preparing cementitious materials by compounding silicon-manganese slag micro-powder with ordinary Portland cement and admixtures, and improve the comprehensive utilization rate of silicon-manganese slag, Method silicon manganese slag powder A, silicon manganese slag powder B, ordinary Portland cement 42.5 were used as raw materials, and high-performance admixtures were mixed to prepare silicon manganese slag-based cementitious materials. The mechanical properties of the specimens were tested according to 《Composite Admixtures for Concrete》 (JG/T 486-2015) and《Cement Sand Strength Test Method (ISO Method)》(GB/T17671-2021). A variety of characterization methods were used to test the mineral composition, chemical composition, micromorphology and thermal stability of the samples. Result The 7 d flexural strength activity index of silicomanganese slag-based cementitious materials was higher than 110%, the 7 d compressive strength activity index was 87.24%～90.98%, the 28 d flexural strength activity index was 87.01%～93.51%, and the 28 d compressive strength activity index was 87.34%～91.85%, which was much higher than the mechanical properties of the first level of "Composite Admixtures for Concrete" (JG/T 486-2015). On the one hand, silicon manganese slag powder and ordinary Portland cement 42.5 form SiO₂-Al₂O₃-CaO cement system, on the other hand, the sulfate in the admixture stimulates the gelling activity of silicomanganese slag powder, thereby improving the mechanical properties of silicomanganese slag-based cementitious materials, especially the early flexural strength and the later compressive strength. ConclusionThe formula of silicon-manganese slag-based cementitious material is Ordinary Portland cement 42.5 dosage of 315 g, silicon-manganese slag powder A dosage of 115～125 g and admixture dosage of 10～20 g, and its mechanical properties are the best.