Organic precursor of EP/PU was prepared by epoxy resin which was polyurethane toughened, and then modified epoxy resin adhesive was synthesized using nano-silica as modifier. Microstructure of composite materials was observed by scanning electron microscopy (SEM), the results showed that the inorganic phase had good compatibility in polymer matrix, and polyurethane in epoxy resin have formed the "island structure". The mechanical properties, thermal stability and dielectric loss, dielectric constant of composites were investigated. The results indicated that doping of appropriate amount of nano-silica could improve mechanical property, shear strength and impact strength of 2wt% SiO2/EP-PU were increased 173% and 106.67%, than that of pre-doping of composite, respectively. Thermal decomposition temperature (Td) was increased, Td of 2wt%SiO2/EP-PU was increased 8.1°C than that of pre-doped of material. Dielectric constant (ε) was as follows: was decreased with the increase of frequency, but increased with the increase of inorganic component, dielectric loss (tanδ) was increased with the increase of frequency and inorganic doping.