Abstract: According to the cement compositing principle, the composite Portland cement, CSA cement and dihydrate gypsum were selected to be proportioning tested, in order to research the hydration mechanism, hydration products characteristics and main index of performance, eventually the optimal proportion of composite cementing material was got. Experimental results show that the main early hydration product was AFt, which made the cement set rapidly and results in the high early mechanical strength. The main mid and last hydration products were CSH gel and CH gel, which were interlaced with AFt and increased the compressive strength of material. Water requirement of normal consistency was increased with the addition of CSA cement and dihydrate gypsum. The setting time was shortened with CSA cement and dihydrate gypsum increases. The compressive strength were higher than the base composite Portland cement. The optimal proportion of composite cementing material is that CSA cement dosage should not be more than 15% and the dihydrate gypsum dosage should not exceed 10%. The indicates of paste filling material made by the composite cementing material meet the engineering needs.