Developing of high-grade cementitious materials with lower clinker content is one of the most effective ways for the peak carbon dioxide emissions in cement industry, which proposes a higher requirement for the utilization of admixtures and the synergistic effect of different admixtures. In this study, clinker-silicomanganese slag-limestone compound cementitious materials were prepared by using local industrial solid waste silicomanganese slag and a rich resource of limestone in Sichuan province. Properties and hydration characteristics of compound cementitious materials were studied. The results show that the clinker-silicomanganese slag-limestone compound cementitious materials have proper workability and significantly improved later-stage mechanical properties. The problems of prolonged setting time and early strength too low in compound cementitious materials with silicomanganese slag used alone can be effectively improved by the addition of limestone powder. The early nucleation-hydration induction effect of limestone powder and the late hydration activity of silicomanganese slag are fully developed in the clinker-silicomanganese slag-limestone compound cementitious materials system. In addition, synergistical hydration effect of silicomanganese slag and limestone powder can consume aluminum phase to generate the carbonaluminate hydrates, increasing the hydration products and preventing the transformation from AFt to AFm, which is conducive to the stable improvement of the mechanical properties.