Abstract: Modified multi-walled carbon nanotubes suspension(MWCNTs-NH₂(M)) was prepared by modifying on MWCNTs-NH₂. MWCNTs-COOH and MWCNTs-NH₂(M) were dispersed in epoxy(EP) respectively, multiscale MWCNTs-carbon fiber/EP(MWCNTs-CF/EP) composites were successfully manufactured by hot-melt method. The effect of MWCNTs on modulus, toughness of EP and interfacial shear strength (IFSS) between EP and CF was investigated, the reactions between MWCNTs and the sizing agent of CF were analysed, and the mechanical properties of multiscale MWCNTs-CF/EP composites were evaluated. The results indicate that functional MWCNTs can strengthen modulus and toughness of EP more effectively. The IFSSs are improved due to the chemical reactions between -COOH or -NH₂ grafted on the MWCNTs surface and the epoxy group in the sizing agent of CF. The multiscale MWCNTs-CF/EP composites show an improved mechanical behavior and this effect is more evident with MWCNTs-NH₂(M) compared to MWCNTs-COOH, the 0° compressive strength, 90° compressive strength, flexural strength, flexural modulus, compression strength after impact(CAI) of multiscale MWCNTs-CF/EP composites can be enhanced by 16.7%, 16.3%, 40.9%, 30.3%, 20.6%, respectively when the mass fraction of MWCNTs-NH₂(M) is 1wt%.