Epoxy resin was modified by MWNTs and hot-melt prepreg reinforced by carbon fiber was manufactured.The effects of the modification methods，specifications and contents of MWNTs on rheology characteristic of resin matrix and the mechanical properties of carbon fiber composites were investigated.The results show that the viscosity of modified resin increases more evidently when the diameter of MWNTs is smaller,the difficulties of fabricating process reduce as compatibilizer is put in.The toughening effect of high ratio of MWNTs is better than that of low ratio NWNTs.As the content of MWNT-NH₂(b) increases,the 0°,90° compressive strength,interlaminar shear strength and CAI of carbon fiber/epoxy composites improve primarily and reduce subsequently.When the content of MWNT-NH₂(b) is 2wt%,the above mechanical properties are optimal,and the 0°,90°compressive moduli-enhance gradually.Pull-out and fracture,bridging and crack deflexion are the main action mechanisms of carbon nanotubes in the carbon fiber/epoxy composites.