Abstract: Agricultural non-point source pollution is more serious in agricultural pollution. As reported, agricultural non-point source pollution has become one of the most important environmental problem in China and all around the world. An ecological ditch with submersible dam in it was adopted to research the removal mechanism of nitrogen and phosphorus through aquatic plants and fillers and the effects of different factors. The results showed that:（1）The interception effect of ditch with submersible dam is superior to that of blank ditch and plant ditch.（2）the nitrogen and phosphorus removal effect is best in the condition of high concentration（TN = 30 mg/L, TP = 0.9 mg/L）, low flow （50 L/h）and medium water level （16 cm）.（3）The difference of the filling position of the two ditches has little effect on the removal efficiency of nitrogen and phosphorus. Thus, the ecological ditch with submersible dams played an important role in the interception of nitrogen and phosphorus in farmland drainage.

Key words: non-point source pollution, ecological ditch, nitrogen and phosphorus interception, concentration