The nitrogen surplus of the upstream agricultural land have a great impact on the eutrophication of the Lake Taihu. Based on the suburban agricultural data of the year 2002, the nitrogen surplus was calculated for the agricultural land of the upstream Taihu. The calculation results show that the agricultural land has a total surplus of 134. 8 x 10³ t/a, and the kilogram surplus per hectare agricultural land is 178. 9 kg per year. The east and west Tiaoxi catchments have lower surplus values less than 130 kg/( hm² · a)，but the other regions have higher values. According to the long calculated series of the N-surplus in the case-study region, the long-term N-surplus changes for the whole upstream area of the Lake Taihu are analyzed in the paper. At last, the authors upstream agricultural land.