Mg-doped on core-shell structured layered oxide LiNi0.6Co0.2Mn0.2O2 cathodes are synthesized by doping Mg into LiNi0.8Co0.1Mn0.1O2 core and LiNi0.2Co0.4Mn0.4 O2 shell，respectively or Mg co-doped both in core and shell. The influence of Mg doping on crystal structure are characterized by XRD，EDS，XPS and ICP-ES. Electrochemical tests show that doping Mg in the shell layer of Li[(Ni0.8Co0.1Mn0.1)2/3(Ni0.2Co0.4Mn0.4)1/3]O2 (S–Mg) exhibits the optimized electrochemical performance, with retention of 85.79% after 100 cycles at 0.2 C and a high discharge capacity of 128.4 mAh g−1 at 5 C, compared with C–S, C–Mg, and F–Mg cathodes. Mg-doped in shell layer of Ni-rich cathode material LiNi0.6Mn0.2Co0.2O2 can not only maintains the stability of material surface, but also reduces the material impedance. The expansion space of the crystalline host lattice caused by Mg doping in the shell will also promote the transport of Li+ during charging and discharging. Cation doping in shell is conductive to electrochemical performance of core-shell materials.