Composites of reduced graphene oxide (rGO) and layered LiMnO2 (LiMnO2@rGO) were successfully synthesized and demonstrated via a one-pot hydrothermal route at a temperature of 200 °C for 12 h. The obtained LiMnO2@rGO was characterized by x-ray diffraction, transmission electron microscopy, Fourier transform infrared spectra and Raman spectra. Electrochemical performance tests of LiMnO2@rGO and LiMnO2 cathodes exhibited that after graphene oxide was loaded, the discharge capacity and cycling performance were greatly improved, the maximum discharge capacity reached 185.6 mAh g-1 at the current density of 100 mA g-1 with retention capacity higher than 80% even after 100 cycles between 2 and 4.5 V vs. Li+/Li, which is much better than most previous reports (table S1). The principles of the corresponding phenomenon were fully explained by the low electron conductivity, high structural stability and lithium diffusion coefficient of LiMnO2@rGO, which was also proved by cyclic voltammetry testing, electrochemical impedance spectroscopy and relevant equivalent circuit fitting. This work not only provides significant insights into the relationship between the structure and electrochemical performance of electrodes, but also shows the great potential of LiMnO2@rGO composite electrodes applied as the cathode materials of lithium-ion batteries.