Abstract: A simulated horizontal subsurface-flowed constructed wetland was set up in laboratory to study the water quality out from the wetland in horizontal distribution uniformity condition. Four scenarios were set to analyze the removal efficiency of COD, TN and TP in order to determine the optimal hydraulic retention time (HRT). Results showed that the average removal rate of wetlands to COD, TN and TP was 54.04%, 65.83% and 80.79% when the HRT was 3 days; the average removal rate of wetlands to COD, TN and TP was 75.93%, 74.97% and 77.34% when the HRT was 2 days, the average removal of constructed wetlands to COD, TN and TP were 73.19%, 56.20% and 73.36% when HRT was 1 day; the average removal of constructed wetlands to COD, TN and TP was 46.46%, 34.91% and 47.04% when HRT was 0.5 day. If only concerning wetland water quality, the HRT of 2 days would guarantee effluent quality meet the standard Ⅴ class of‘Surface Water Quality Standard (GB 3838-2002)’.