Abstract: In this study, a cement-steel slag-based grouting material was developed and investigated how its material composition influenced its early-age performance was investigated so as to promote low cost and high performance in tunnel grouting materials. The water-to-binder ratio, steel slag mass fraction and superplasticizer mass fraction were ajusted to analyze the evolution patterns of the rheological behavior, compressive strength, fluidity, and microstructure of the grouting material. Results show that: ① increasing water-to-binder ratio led to decreasing 1-day and 3-day compressive strength due to reduced hydration products and the formation of larger pores, while superplasticizer improved the early strength by optimizing the distribution of hydration products; ② a small addition of steel slag (8%) accelerated hydration, whereas excessive slag (16%) impaired the continuity and stability of hydration crystals; ③ the yield stress, plastic viscosity, and thixotropy decreased with increasing water-to-binder ratio and superplasticizer mass fraction but increased with higher slag mass fraction; ④ an optimized water-to-binder ratio (≤0.5) and slag mass fraction (≤16%) effectively refined the pore structure and enhanced both the early and long-term mechanical properties, while a moderate superplasticizer dosage (≤1.5%) improved the rheological behavior and material stability.