The bio-rack is a new approach for treating low-concentration polluted river water in wetland systems.A comparative study of the efficiency of contaminant removal between four plant species in bio-rack wetlands and between a bio-rack system and control system was conducted on a small-scale (500 mm length × 400 mm width × 400 mm height) to evaluate the decontamination effects of four different wedand plants.There was generally a significant difference in the removal of total nitrogen (TN),ammonia nitrogen (NH3-N) and total phosphorus (TP),but no significant difference in the removal of permanganate index (CODMn) between the bio-rack wetland and control system.Bio-rack wetland planted with Thalia dealbata had higher nutrient removal rates than wetlands planted with other species.Plant fine-root (root diameter ≤ 3 mm) biomass rather than total plant biomass was related to nutrient removal efficiency.The study suggested that the nutrient removal rates are influenced by plant species,and high fine-root biomass is an important factor in selecting highly effective wetland plants for a bio-rack system.According to the mass balance,the TN and TP removal were in the range of 61.03-73.27 g/m2 and 4.14-5.20 g/m2 in four bio-rack wetlands during the whole operational period.The N and P removal by plant uptake constituted 34.9％-43.81％ of the mass N removal and 62.05％-74.81％ of the mass P removal.The study showed that the nitrification/denitrification process and plant uptake process are major removal pathways for TN,while plant uptake is an effective removal pathway for TP.