The typical sol-gel method was adopted to synthesize the pristine Li-1.20[Mn0.54Ni0.13Co0.13]O-2 and Li-1.20[Mn0.54-xNi0.13Co0.13Nbx]O1.95F0.05 = 0, 0.01, 0.02, 0.03). And the effects of Nb5+ and F- substitution on the lattice structures, particles morphologies and electrochemical properties were comprehensively studied by using the Xray Diffractometer (XRD), Scanning Electron Microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and galvanostatic charge-discharge tests. The results demonstrated that the Nb5+ and F- doping modification could increase the lattice parameter of a and c, and would not obviously change the morphologies of cathode particles. Besides, the electrochemical properties of Li-1.20[Mn0.54Ni0.13Co0.13]O-2 were significantly improved after the Nb5+ and F- doping. Among all samples, the Li-1.20[Mn0.52Ni0.13Co0.13Nb0.02]O1.95F0.05 delivered the highest discharge capacity of 117.1 mAh g(-1) at 5C high rate and the most stable capacity retention of 92.5% at 0.5C rate after 200 cycles. The Electronic Impedance Spectroscopy (EIS) analysis reflected that the Nb5+ and F- doping could relieve the increase of charge transfer resistance and the ohmic resistance of interaction between electrolyte and cathode during cycling.