Abstract:In order to find out the whole riparian buffer system denitrification effect and various types of riparian buffer in the system, studied under a certain concentration of pollution load impact riparian buffer area TN(total nitrogen), NO3--N (nitrate nitrogen), NO2--N (nitrite nitrogen) and NH4 -N (ammonia nitrogen) purification mechanism by engineering-scale fields test on site. The results showed that farmland is an important source of lake reservoir water nonpoint source pollutants, Other different forms of vegetation filter can effectively gather, absorb pollutants. Among them, tree grass composite filtration zone has better effect of nitrogen removal than a single herb filtration zone ,tree grass composite filtration zone with TN,NO3--N,NO2--N and NH4 -N quality concentration subtractive rate was 84.21%, 51.61%,17.61% and 71.98%. And the quality concentration subtractive rate in single herb filtration zone was just 37.44%, 49.60%, 6.72% and 74.45% .In addition, Reed plant-based filter with a water plant of agricultural non-point source pollution has good control effect, the end removal ratio of runoff TN,NO3--N,NO2--N and NH4 -N , was 82.77%, 36.40%, 37.82% and 74.54%.