To explore the influence mechanism of dolomite powder on the macroscopic properties and microstructure of cement, the hydration heat, fluidity, compressive strength, and mercury intrusion porosimetry (MIP) of dolomite powder-cement composite cementitious with different contents were conducted on. The results indicated that the addition of dolomite powder could significantly reduce the hydration release rate and cumulative heat, delay the appearance of the exothermic peak. Dolomite powder increased the fluidity of the cement paste, but excessive dolomite powder led to bleeding and segregation of the cement paste. Dolomite powder reduced the strength of the composite cementitious, and the decrease in compressive strength become more obvious as the content increases. However, the negative impact of dolomite powder on compressive strength of cement could be reduce by prolonging curing age. The effect of dolomite powder on the porosity and median pore diameter of long curing age cement was weak within 20% of the content of dolomite powder. The low dosage of dolomite powder showed a relatively small influence on the porosity, median pore size and the proportion of above 50 nm pore of long-age cement. However, the porosity, median pore size and the proportion of above 50 nm pore were increased significantly by adding excessive dolomite powder, and the compressive strength was decreased significantly.