LiNi1/3Co1/3Mn1/3O2, a cathode material for Li-ion battery, has the advantages of large discharge specific capacity, good thermal stability, low cost, and good safety performance, but its rate performance needs to be further improved. Therefore, K+ doped LiNi1/3Co1/3Mn1/3O2 materials (LNCM-xK) were prepared by hydrothermal method in this paper. The morphology and structure of LNCM-xK were characterized by X-ray diffraction spectrum, field emission scanning electron microscopy and X-ray photoelectron spectroscopy, and its electrochemical properties were tested by electrochemical workstation and blue electric test system. The results show that K+ doping can effectively reduce the cation mixing degree and effectively improve the electrochemical properties of LiNi1/3Co1/3Mn1/3O2 materials, among which K+ doped LiNi1/3Co1/3Mn1/3O2 (LNCM-0.125K) of x=0.125 has the lowest cation mixing degree. The LNCM-0.125K sample has the best electrochemical performance. The capacity retention rate is 96.15% after 50 cycles at 0.2 C. The rate performance is carried out at different current density (0.2 C, 0.5 C, 1 C, 2 C, 5 C), and the capacity retention rate is 97.00% after 30 cycles of continuous charge and discharge.