Over nitrogen-fertilization often results in a low nitrogen use efficiency (NUE) and high N loss in Tai lake region. In order to find an optimal N application amount to rice and wheat, field experiments were conducted under different N application amounts from 2004 to 2006. The results showed the crop yield response to added N was very low when N amount exceeded 150 kg/hm2, and the mean nitrogen uptake efficiency (REN) ranged from 32.41% to 46.11% in three years for rice and from 27. 8% to 36.0% in two years for wheat when N rate was 100 to 350 kg/hm2, and the corresponding nitrogen agronomy efficiency (AEN) ranged from 5.56 kg/kg to 14.95 kg/kg for rice and from 6.91 kg/kg to 17.1 kg/kg for wheat. The study also indicated that REN, nitrogen physiological efficiency (PEN), AEN, and partial factor productivity of applied N (PFPN) were 37.6%, 29.5 kg/kg, 11.0 kg/kg and 44.5 kg/kg respectively for rice with N application amount of 209 kg/hm2 and were 31.4%, 38.4 kg/kg, 12.0 kg/kg and 23.7 kg/kg with N application amount of 219 kg/hm2 for wheat respectively. We concluded that the optimal N application amount could not only increase crop yields but also increase the farmer’s benefits.