In order to meet the requirements of advanced treatment of effluent from biochemical treatment of printing and dyeing wastewater,activated carbon (AC) particles loaded with manganese dioxide were prepared by impregnation and thermal reduction method. The morphology and structure of the modified activated carbon (AC-Mn and AC-O-Mn) were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy. In a three-dimensional electrode system, the effect of modified activated carbon particle electrode on the degradation of COD in the effluent from biochemical treatment of printing and dyeing wastewater was investigated. The results showed that manganese-loaded activated carbon particle electrode with a loading amount of 4.4% could be prepared using manganese sulfate as the precursor. The main form of manganese in activated carbon was manganese dioxide. Oxidation destroyed the structure of activated carbon and was not conducive to the loading of manganese dioxide. The effluent from biochemical treatment of printing and dyeing wastewater was treated by the three-dimensional electrode system. After 15 minutes of electrolysis, the concentration of COD was reduced to 47 mg /L,and the removal rate of COD could reach 83.7% which was 41% higher than that with unmodified activated carbon particle electrode.