Abstract: Genotype differences for nitrogen use efficiency have been found in cereal crops, including rice, wheat, and corn, et al. Genotype differences for nitrogen use efficiency result from the differences for uptake efficiency and utilization efficiency of nitrogen. Kinetic parameter of N uptake, root morphology, and functional period of the root system affect uptake efficiency,and utilization efficiency is a combined result of several physiological processes, including nitrogen assimilation, transference and photosynthesis.Analysis of the mechanism behind genotype differences for nitrogen use efficiency can increase nitrogen utilization efficiency, decrease the loss of nitrogen. Therefore,higher yields with less nitrogen fertilizer can be reached,thus resulting in a sustainable agriculture, reducing the input of the agricultural production, and protecting the eco-environment.