In this paper, the removal of TP and TN and the transformation of nitrogen (starting with NH3-N, NO2-N and NO3-N) by a type of flow that has been put into constructed wetland under different hydraulic retention time are studied, so that effective data are obtained, and corresponding improvements are made for river pollution control, and reasonable hydraulic retention time is given. The research shows that the subsurface flow structure wetland has great potential to remove TN from polluted water, and the longer the hydraulic retention time, the more obvious the removal effect, but the removal effect of TP is generally not high. At the same time, the reasons are analyzed and the corresponding improvement methods are put forward.

Keywords: hydraulic retention time; Undercurrent wetland; Total phosphorus; total nitrogen