Abstract: N is the necessary nutrition for plant growth and NH₄⁺,NO₃^- are two major forms when N is absorbed by plants. NH₄⁺ and NO₃^- in wet deposition are two very important factors to compensate the N loss of agricultural ecosystem. In order to learn the situation of N in the wet deposition of Shanghai District and its effects on agricultural ecosystem in this area, the amount, forms and ecological effects of N in the wet deposition were studied. Results show that in recent years, the content of N nutrition in the precipitation is fairly high in the region, among which NO₃^-> is 2.587mg/L,NH₄⁺ 2.155mg/L and TIN more than 4.000mg/L. The N imported to the agriculture ecosystem of the area by wet deposition is abundant, with 26.580kg/hm²·a NH₄⁺. In 1999, NH₄⁺ was 38.930kg/hm², NO₃^- was 31.545kg/hm². The average annual TIN imported from wet deposition is 58.123kg/hm²·a equal to 124.549kg/hm²·a CO(NH₂)₂ or 327.980kg/hm²·a NH₄HCO₃ and in 1999 the quantity of TIN was 77.750kg/hm² equal to 166.607kg/hm² CO(NH₂)₂ or 438.732kg/hm² NH₄HCO₃, accouting for 35% of the national average application amount of fertilizer(N) in 1998.