The water purification demonstration project of a multi-stage bypass constructed wetland beside Nanfei River, including a pretreatment unit, vertical flow constructed wetland unit and horizontal flow constructed wetland unit, was built to reduce pollutants from Nanfei River into Lake Chaohu. From March 2014 to February 2015, the concentrations of the pollutants were detected from each purification unit and removal efficiencies of each constructed wetland unit were examined. The results showed that a multi-stage bypass constructed wetland reflected a higher removal efficiency. The total removal rates of COD_Mn, total nitrogen(TN), ammonium nitrogen(NH⁺₄-N) and total phosphorus(TP) reached 70.9%, 43.7%, 43.5% and 76.6%, respectively. COD_Mn and TP of the effluent attained the Environmental Quality Standard for Surface Water (GB 38382002) Ⅳ, while NH₄⁺-N of the effluent meet the needs of Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant Pollutant (GB 189182002) class 1 A. There were significant differences on the pollutant removal efficiency among different purification units, the pretreatment unit played a leading role in removing COD_Mn, with a 65.1% reduction for COD_Mn; while TN, NH₄⁺-N and TP were degraded mainly in the vertical flow constructed wetland unit, which contributed 23.2%, 27.1% and 51.1% respectively to the total removal of TN, NH₄⁺-N and TP. The removal efficiencies of the studied pollutants varied with the seasons. The removal rate of COD_Mn and TP decreased in sequence of summer> autumn> spring> winter, while the removal rate of TN decreased in sequence of autumn> spring> summer> winter and the removal rate of NH₄⁺-N was in the order of autumn> summer> spring> winter. Finally, in order to improve the denitrification efficiency recommended by adding carbon source and increasing the hydraulic retention time to further optimize the process.