Abstract: The effects of nitrogen rates on photosynthetic characteristics and yield of high-yielding cotton in Xinjiang were investigated with two cotton varieties, Xinluzao 6 and Xinluzao 7. The result showed that proper nitrogen rate (N 300kg/hm2) could improve photosynthetic characteristics of cotton, the chlorophyll content, nitrate reductase (NR) activity and net photosynthesis rate (Pn) of the middle and bottom leaf raised at later growth stages. The activity of PSⅡ (Fv/Fo), maximum photochemical efficiency of PSⅡ (Fv/Fm) were maintained at a relatively high level. Therefore, the physiological activity in middle and bottom leaves of cotton was raised,and senescence of leaf delayed, photosynthetic product was sufficiency during the later growth stages, finally it could lead to increase of yields of lint. But this kind of improvement on physiological function depended on cultivars and growth stages. The chlorophyll content, NR activity, Pn, Fv/Fo and Fv/Fm of Xinluzao 6 increased with the increasing of nitrogen application at the earlier stages, these indices were maintained at a relatively high in the treatment of N 300kg/hm2 at the later stages,but it remained low in the treatment of N 450 kg/hm2,because excessive nitrogen application was apt to result cotton vain growing in full flowering, subsequently led to rapid decline in net photosynthesis rate. Therefore, according to change of varieties and growth stages of cotton, nitrogen application should be moderated, avoid high amount lead to decrease of yields of lint and waste of fertilizer in the later growth stages.