SiO 2 @PEGMA composites were synthesized by grafting poly(ethylene glycol) methacrylate (PEGMA) on SiO 2 nanoparticles via radical polymerization. The chemical structures of the SiO 2 @PEGMA composites were analyzed by Fourier transform infrared, 1 H NMR, and transmission electron microscopy methods. The mechanical and fresh properties, hydration products, heat of hydration, microtopography, and pore structures were studied. The shell formed by the grafted PEGMA gave the SiO 2 @PEGMA composite a steric hindrance effect, which enabled it to have excellent dispersion stability even in the cement pore solution. The SiO 2 @PEGMA composites could not only effectively facilitate hydration reaction and generate calcium silicate hydrate (C-S-H) through the seeding effect but also make the pore structure more compact by the filling effect. Compared with other control groups, SiO 2 @PEGMA composites could obviously enhance the compressive strength of cement samples, which was increased by 36.7% after curing for 28 days.