Abstract: The research for studying the Xinjiang arid region on photosynthesis characters of Xinhai 14 Long-fibre Cotton under conditions of five artificial irrigation droughts. The result showed under the different conditions of irrigation , when W was 7650m3/hm2 , the curve of diurnal variation of leaf photosynthesis showed single peak, with the irrigation quantity dropping .The curve of diurnal variation of leaf photosynthesis showed two single peak. The light compensation point of photosynthesis of Xinhai 14 Long-fibre Cotton leaves were 50μmol/m2·s；when W were 2850m3/hm2，the light saturation point of photosynthesis of Xinhai 14 Long-fibre Cotton leaves were 310μmol/m2·s , when the W was 5475m3/hm2 and over the light saturation point were 1280μmol/m2·s.The leaf net photosynthesis(Pn) rate and transpiration rate increased with the raise of irrigation quantity，the stoma resistance drooped with the raise of irrigation quantity. The water use effciency(WUE) raised with the dropping of irrigation quantity. The yield of cotton was the most sensitive to irrigation quantity.Positive correlation appeared between the net photosynthetic rate and transpiration rate .There was a significant negative correlation between Pn and the stoma resistance. The optimum irrigation quantity of Pn was 6945 m3/hm2，at which the plant needs irrigation quantity，was 5250m3/hm2.