In the present study, silane coupling agents (SCAs) were used as admixture in cement paste. The influence on the cement hydration in different stages as well as the mechanical properties were well investigated. Results demonstrated that silanes play a role of retardant in cement paste at the very early age, the proposed mechanism laid in the attraction force between the intermediate hydrolysis products of silanes and the cement hydrated products. The intermediate hydrolysis products can form a gel-like barrier covering the cement hydrated products and were further proved by the designed pre-hydrolysis experiments using calorimeter and Fourier transform infrared spectroscopy (FTIR). However, cement paste modified by silane would have denser structure compared to neat paste as a result of reaction between polycondensated silane and CH after 28 days of curing, leading lower porosity, higher hydration degree and better mechanical performance.