In this study we measured changes in the COD_Cr, TN, NH₄⁺-N, TP, and DO concentrations and the pH of different layers in an integrated vertical-flow constructed wetland (IVCW) treating eutrophic water. We also examined the composition and diversity of the bacterial community in the IVCW using PCR-DGGE. Our results showed that most of the contaminants were removed during sewage flow from the down-flow chamber to the up-flow chamber. The removal rates of TN, TP, COD_Cr, and NH₄⁺-N were, respectively, 63.7%, 66.7%, 72.2%, and 67.9% in the down-flow; consequently, the COD_Cr and TP concentrations of the effluent fell below 10 mg/L and 0.05 mg/L. There were some common microorganisms and specific microorganisms in the different layers of the constructed wetland because of the changes in environmental factors and nutrient levels. The diversity of the bacterial community was highest in the upper layer of the down-flow system, and the similarity in the down-flow system was higher than that in the up-flow system. From the down-flow system to the up-flow system, the diversity of the bacterial community increased from 2.31 to 1.95 and the structural similarity gradually increased from 65.7% to 70.9%. The higher complexity of the bacterial community in the upper layer of the constructed wetland may be supported by plant oxygenation, rhizodeposition, and litter accumulation.