The effects of sodium aluminate(SA), superplasticizer(Sp) and super absorbent polymer(SAP) on strength and hydration characteristics of hardened cement paste from the view of pore structure were investigated to reveal the correlation between microstructure of hardened cement paste and their macroscopic properties. The results show that the maximum exothermic peak is significantly enhanced in acceleration period of cement hydration. Depending on dissolution precipitation of SA, dispersion of Sp and function of SAP as reservoir, the hydration rate in early ages, hydration area and hydration degree in late ages are improved. The compressive strength of modified cement paste at 28d reaches 178 times higher than that of 7d, which reveals that the late mechanical properties of cement based grouting materials with accelerator can be improved by the moderating effect of admixtures. While the threshold dosage of SAP after releasing water leads to degradation of pore structure and mechanical properties. Uniformity of average pore radius for different admixture systems and their compressive strength at 28d show that the characteristics of mechanical properties can be reflected efficiently by the pore size distribution.