Using lysimeter experiment we studied nitrogen leaching from paddy field in wheat growing season under different fertilizer application levels and treatments in Taihu lake area. Results showed that nitrogen was leached mainly in the form of NO_3~--N, and it was 36.2%-99.1% of the total leached nitrogen, with average of 82.9%. Different fertilizer application levels and treatments had different effect on nitrogen leaching. Under the experiment level, nitrogen leaching could bring potential pollution to underground water.