In order to achieve the precursor nanofiber of nano-carbon fibers with integrated structure and good properties, hybrid polyacrylonitrile (PAN) nanofibers with different loading of carboxylated multi-walled carbon nanotubes(MWCNTs) were fabricated through electrospinning. Scanning electron microscopy(SEM), polarized FTIR spectroscopy, transmission electron microscopy(TEM), Raman spectroscopy and the tensile test were adopted to study the microstructure and mechanical property of the hybrid nanofiber. The diameter of PAN nanofibers was decreasing with the adding of MWCNTs, but the sample containing 5% (mass fraction) MWCNTs displayed a diameter mutation. The experimental results showed that adding MWCNTs into the polymer was propitious for the orientation of molecular chains. Most of MWCNTs embedded in the PAN. and aligned along the fiber axis. When the concentration of MWCNTs was below 5%, the tensile strength and modulus of PAN nanofibers were both enhanced with the loading of MWCNTs, which respectively reached to 88.6 MPa and 3.21 GPa after adding 3% MWCNTs.