Abstract: 【Objective】Study on designing the tax of nitrogen fertilizer can provide one of the new ways for controlling nitrogen fertilizer non-point source pollution. 【Method】The tax design of nitrogen fertilizer was discussed by utilizing the external theory and the demand elasticity theory.【Result】The results showed that the 11 counties (cities and districts) which the farmland nitrogen application in the Dongting Lake area surpassed the average ecological fertilization dosage are listed to the taxation scope of nitrogen fertilizer tax, the ecological environment loss will reduce 0.07×108 Yuan and the revenue will increase 0.89×108 Yuan in the country after levying on nitrogen fertilizer. The economic benefits, which brought about by the increasing of the food supplies production, will be 0.58×108 Yuan and the net social benefit will be 1.58×108 Yuan after the revenue collecting. The variation scope of the increasing expenditure of farmers will range from 0.95％ to 1.49％. The increasing income of farmers will take up -5.93％ to 8.41％ of the net total income. The 6 counties (cities or districts), Huarong, Miluo, Anxiang, Lixian, Nanxian and Yuanjiang, in which the nitrogen application surpassed the ecological fertilization dosage and decreases the food supplies production are listed to the N fertilizer tax collecting scope, the ecological environment loss will reduce 0.06×108 Yuan and the revenue will increase 0.49×108 Yuan in the country after levying on nitrogen fertilizer. The economic benefits, which brought about by the increasing of the cereals production, will be 1.25×108 Yuan and the net social benefit will be 1.85×108 Yuan after the revenue collecting. The variation scope of the increasing expenditure of farmers will range from 1.01％ to1.49％. The increasing income of farmers will take up 2.57％ to 8.41％ of the net total income. The coefficient of price elasticity of nitrogen fertilizer demand is 0.21, which instructed that the market demand and supply are in lack of elasticity in the short period and the impact of nitrogen Fertilizer manufacturers is subtle. 【Conclusion】Considering from the entire social welfare, taxation of nitrogen fertilizer will have more advantages than the disadvantages in the Dongting Lake area. It is more appropriate to list the Nitrogen application surpassing the average ecological fertilization dosage and the food supplies production not decreasing areas as the nitrogen fertilizer tax collecting scope.

Key words: Nitrogen fertilizer, Non-point source pollution, Tax, The Dongting Lake area