Abstract: The carboxyl carboxyl nitrile rubber (CTBN) and nano-silica (nano SiO₂) were used as toughening agents, the copolymer of CTBN and epoxy resin (EP) were prepared as an emulsion by reverse transfer, followed by addition of nano SiO₂ for blending. Finally, the curing agent was added to prepare the nano SiO₂-CTBN modified water-based EP(nano SiO₂-CTBN/WEP) composite by gradient heating. The properties of the nano SiO₂-CTBN/WEPcomposite were characterized by an FTIR, SEM, TEM, universal tensile tester and TGA. The results show that:when the CTBN mass fraction is 20%(mass ratio to EP E-51), the prepared CTBN/WEP emulsion exhibites better storage stability. The addition of 3% nano SiO₂ in CTBN/WEP resultes in the best effect of toughening. The tensile strength is 14.5 MPa, the elongation at break is 9.1%, the impact strength is 11.3 kJ/m² and the flexural strength is 22.4 MPa, which increase by 40.1%, 27.4%, 73.9% and 72.7%, respectively, compared with the CTBN/WEP sample without adding of nano SiO₂. The initial thermal decomposition temperature of the nano SiO₂-CTBN/WEP also increases by nearly 25℃.