The discharge of urban sewage and agricultural non-point source pollutants is the main reason causing eutrophication in gullies in most cities of northern China. Based on a careful analysis on the ecological structure and ecological characteristics of a gully, this article preliminarily studies the interception and degradation mechanisms of nitrogen pollutants by the gully. Meanwhile, to take gullies in Changchun as the object of the study, this article carries out an experiment on the interception effect of nitrogen pollutants by gullies. This experiment respectively establishes a control section in the upper and lower reaches of a gully, and takes water samples four times in each section from May to August to determine total nitrogen, total phosphorus, nitrate nitrogen, ammonia nitrogen and salinity. The result shows: the gully plays some role in the interception of pollutants; total phosphorus accounts for the largest interception in pollutants in the experimented gully section, with the relative interception rate of 27.46%, followed by ammonia nitrogen, with the interception rate of 21.80%, which is the result of the combined effects of aquatic plants, microorganisms and sediment in the gully.