Aiming to reveal the response of nitrogen uptake and transformation under different water and nitrogen conditions at pre and postflower, meanwhile to investigate the relationship between crop nitrogen, fertilizer nitrogen, soil nitrogen and dry matter absorption and transport. Based on the 15N isotope tracing technique, the experiment with three irrigation levels (W1:40mm, W2:60mm, W3:80mm) and four nitrogen levels (N0:0kg/hm2, N1:180kg/hm2, N2:240kg/hm2, and N3:300kg/hm2) were carried out in field conditions. The results showed that the nitrogen fertilizer recovery rate was 21.27%~44.64%, and the best value was obtained in N2W2 plot. If making a comparison of nitrogen accumulation in each organ at maturity stage, the best was in grain, then was in leaf, stem, and the last was in ear leaf. With moderate nitrogen application regime, the nitrogen accumulation in plants was the highest, however, in W1 plot, it was significantly decreased (P<0.05). The order of nitrogen transformation rate from the largest to the smallest was leaf, stem and ear leaf. The best nitrogen transformation rate was achieved with N2W2 practice which was significantly different from other treatments (P<0.05). The amount of soil nitrogen involved in transformation was greater than the amount of fertilizer nitrogen. The 15N transformation and soil nitrogen transformation of various organs of maize from the largest to the smallest was leaf, stem, and stem leaves. Totally 22.43% ~ 39.45% of nitrogen transformation in plant came from fertilizers, the moderate water and nitrogen treatment could keep higher soil nitrogen transformation. The order of contribution rate of nitrogen grain in different organs from the largest to the smallest as leaf, stem and ear leaf. Nitrogen transformation in various organ accounted for 18.29%~44.29% of the nitrogen accumulation in the grain, and the N2W2 plot had the best value. Dry matter transformation and grain contribution rate from the largest to the smallest isstem, leaf and spike leaf, and the greatest value was got in N2W2 treatment. Therefore, a clear conclusion was that the irrigation of 60mm and nitrogen application of 240kg/hm2 were the best.