In this paper, a kind of colloidal of nano-silica (CNS) was prepared, which was a comb-like structure polymer. Its main chain synthesized by acrylic acid, polyoxyethylene ether and silane coupling agent, side chain grafted with nano-silica particles. By optimizing the parameters, a reasonable synthesis process and formula were determined. The morphology and particle size distribution of the nano-silica in CNS were characterized by scanning electron microscope (SEM) and dynamic light scattering (DLS). The effects of different amounts of CNS on cement hydration heat, setting time, pore structure, hydration products, mechanical properties and impermeability of concrete were evaluated. The test results show that the addition of CNS can increase the hydration heat release rate, promote the early hydration of cement, accelerate the formation and precipitation of hydration products, increase the hydration temperature and shorten the setting time. The effect on hydration products is that CNS promotes the formation of C-S-H gel at 7 d and reduces the content of Ca(OH)2(CH) in hydration products. At 28 d, CNS accelerates the formation of hydration products and increases the content of CH in hydration products. The macroscopic performance shows that the 7 and 28 d compressive strength and impermeability of concrete are improved.