A novel facile hydrothermal modification method is applied to improve the electrochemical performance of the low-cost cathode material Li1.231Mn0.615Ni0.154O2, which is primarily prepared by a solid-combustion approach. The material before and after modifying are characterized by energy dispersive spectrometer (EDS), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), BET and high-resolution transmission electron microscopy (HRTEM). The samples are served as the cathode of lithium-ion batteries and investigated by galvanostatic experiments within a voltage range 2.0–4.8 V (vs. Li/Li+). The results reveal that the electrochemical performance of the Li1.231Mn0.615Ni0.154O2 cathode electrode is prominently enhanced after modifying. The significantly improved electrochemical performance of the Li1.231Mn0.615Ni0.154O2 cathode is attributed largely to the modification of the surface microstructure and the crystallinity.