In this paper, high-capacity supercapacitor material (Fe-Nx/CNFs) synthesized by electrospinning a metal complex in PAN/DMF solution with different temperatures was presented. Moreover, nitrogen doping (N-doping in short) has been used to tailor the properties of carbon nanofibers and rendered its potential use for capacitor as an effective way. The structural and morphological properties of the Fe-Nx/CNFs were fully characterized and the carbonation temperature of the Fe-Nx/CNFs precursor was optimized. Compared with the pure carbon nanofiber, the annealing temperature of optimized Fe-Nx/CNFs composites electrode material was 550 °C. Fabricating the binder-free iron-based electrode exhibited a higher capacitance of 629 F g−1 at the current density of 1 A g−1 in 4 mol L−1 aqueous KOH electrolyte. Meanwhile, a cycling stability of 97% capacitance retention after cycling 2500 at 5 A g−1 was maintained. This outstanding performance was attributed to the formation of the Fe-N bond and N-doped carbon nanofibers that effectively facilitates electronic transport. Therefore, carbon nanofibers, wherein nitrogen-doped metal (iron) center, exhibited high performance as supercapacitors.