Improving the high rate performance of lithium manganese spinel is one of the key research directions of Li-ion battery. In this study, spinel Li_1.1-xK_xMn₂O₄ (0≤x≤0.03) was synthesized by a high-temperature solid-state method. The results indicate that K⁺ doping significantly improved the high rate performance of the cathode, while the discharge specific capacity of the electrode decreased with the current density increasing. With the optimum doping amount of 1.0% (molar fraction) K⁺, the discharge specific capacity of the cathode increased by 102.8% at 10C (1C=150 mA·g^-1), much higher than that (1.9%) at 0.5C. It can be attributed to the following points: K⁺ doping can firstly expand the cell volume and the Li-O bond length, lower the cation mixing of Li/Mn, and increase the content of carriers (Mn³⁺) of the material. Secondly, K⁺ doping can reduce the electrode polarization and charges transfer resistance, which develops the charge-discharge reversibility, electrical conductivity as well as the diffusion capability of the Li ions for the cathode. Thirdly, K⁺ doping can stabilize the framework of [Mn₂]O₄, degrade the change of internal stress during the electrochemical process, which inhibits the modification of the crystal structure and particle fragmentation. In addition, the existence of K⁺ promotes the agglomeration of the material during the preparation process, which reduces the contact area between the electrolyte and cathode in cell, thereby alleviating the erosion of the electrolyte, as well as the Mn dissolution of the cathode.