Abstract: After having been studying for past several years, the genotype with high effect high response (Xiaoyan22)and the genotype with low effect low response(Xiaoyan6) were screened from 10 local dominating winter wheat varieties (Shan253, Shan229, Xiaoyan 503, Shannong78, Shan225-47, Xiaoyan22, Xiaoyan128, Xiaoyan6, Xinong1043, Xinong2208). Under high, medium and low different nitrogen application rate, the field experiment was conducted to study the NUE difference of two different genotypes Xiaoyan22 and Xiaoyan6 and also study the physiological mechanism by analysing the content of chlorophyll, the NR activity and the photosynthesis daily change in the leaf in key growing stage. The results showed that there were significant differences between two genotypes in the NUE. The NUE of Xiaoyan22 was greater than that of Xiaoyan6.Nitrogen application could improve the NUE of different genotypes. The physiologic mechanism was found that the NR activity, the content of chlorophyll and the photosynthesis of the genotype with high NUE were more than that of one with low NUE in jointing stage.