Abstract: The surface of carbon nanotubes (CNTs) was modified by mixed acid method to obtain carboxylated carbon nanotubes (C-CNTs). SiO₂-coated C-CNTs (C-CNTs@SiO₂) and TiO₂-coated C-CNTs (C-CNTs@TiO₂) were prepared by sol-gel method. Polyaniline-coated C-CNTs (C-CNTs@PANI) were prepared by in-situ polymerization. Four kinds of composites of C-CNTs/EP, C-CNTs@SiO₂/EP, C-CNTs@TiO₂/EP and C-CNTs@PANI/EP were prepared by solution blending with epoxy resin (EP) as the matrix. The results of the study indicate that when the mass fraction of the doped phase is 1 wt%, the impact strengths of the four EP matrix composites are improved to different degrees with respect to the unmodified epoxy resin. When the doping phase content is 7 wt%, the dielectric constants of C-CNTs/EP, C-CNTs@SiO₂/EP, C-CNTs@TiO₂/EP and C-CNTs@PANI/EP composites are 14.1, 7.2, 2.5 and 18.8 times that of the unmodified EP, respectively. At the experimental doping amount, the dielectric losses of C-CNTs@SiO₂/EP and C-CNTs@TiO₂/EP are almost unchanged, and the dielectric loss of C-CNTs@PANI/EP is slightly increased. When the doping phase mass fraction is 1 wt%, the breakdown strengths of C-CNTs@SiO₂/EP and C-CNTs@TiO₂/EP are significantly improved.