Currently, in the Taihu region, the application of N fertilizer in the high-yielding paddy fields of rioewheat double cropping system averages around 520kg N per hectare per year.Experiments for years showed that N fertilization at a rate of 300kg N per hectare per year increased the crop yield significantly by 13.Skg of grain per kg of N applied, with the N recovery rate reaching 40.3%;but the increase was not significant at a rate of 450kg N, and 7.29kg of grain was increased by per kg of N applied with the N recovery rate dropping to 17.2% at a rate of 600kg N per hectare per year. In the last case, the N content in rice straws and sterility grain rate went up while the thousand-grain weight and the yield declined. Consequently, at the current yield level of 10-12 ton per hectare on the high yielding paddy field, the N fertilization rate was recommended to be at 375kg N per hectare per year,which could save 20-30% N-fertilizer as compared with the rate for large-area production.