In order to realize in-situ utilization of weak current generated in microbial fuel cell (MFC), an MFC-EF coupling system was constructed by utilizing the advantages of electro-Fenton (EF) technology. To further improve the performance of the coupling system, a composite cathode of iron and manganese (FeMnO_x/CF composite electrode, CF refers to carbon fiber brush) was prepared, which introduced Fenton-like catalyst manganese on the basis of Fenton catalyst iron. The electrochemical performance of the MFC-EF coupling system and its degradation effect on Rhodamine B (RhB) were investigated by being compared with CF unloaded electrode and Fe&Fe₂O₃/CF composite electrode. Results showed that FeMnO_x/CF composite electrode was successfully loaded with the binary metal oxides of Fe and Mn. The maximum output power of the coupling system was improved (5.47 W/m³), the internal resistance of the MFC was reduced (109.00 Ω), and both the removal rate (91.60%) and mineralization rate (30.84%) of RhB were increased. Besides, the FeMnO_x/CF composite electrode was free from the strict restriction of catholyte pH in conventional Fenton system, and the pH range of catholyte in MFC-EF coupling system was expanded. The study can realize the regeneration and utilization of resources in the process of pollutant removal, which is expected to provide a new idea for practical dye wastewater treatment.