Abstract: The solvent-free nano SiO₂ fluid was prepared with nanoparticle SiO₂ as the core, N,N-didecyl-N-methyl-N-(3-trimethoxysilylpropyl) ammonium chloride (SID3392) as the necklayer and poly(ethylene glycol) 4-nonylphenyl3-sulfopropyl ether potassium salt (PEGS) as the canopy.The solvent-free nano SiO₂ fluid is a Newtonian fluid with low viscosity at room temperature, and its viscosity is 4.3 Pa·s at 26.5 ℃.The mass fraction of SiO₂ in the solvent-free nano SiO₂ fluid is 13.65%.The solvent-free nano SiO₂ fluid is loaded in the epoxy matrix to prepare solvent-free nano SiO₂ fluid/epoxy composites.The TEM results confirm that the solvent-free nano SiO₂ fluid disperses well in the epoxy matrix.DSC test shows that the solvent-free nano SiO₂ fluid can decrease the curing temperature of the epoxy.When the content of solvent-free nano SiO₂ fluid in the composites reaches up to 2.5wt%, the impact properties of the epoxy is improved up to 164.7%.The glass transition temperature is improved by 15.4 ℃.The SEM results of fracture surface also confirm that solvent-free nano SiO₂ fluid can improve the toughness of epoxy.