Abstract: Based on daily data of 25 meteorological stations in North Xinjiang during 1961-2013, the FAO Penman-Monteith equation and crop coefficient method were used to estimate water requirements as well as irrigation water demands of cotton during all growth stages. The results suggested that cotton water requirement in each growth period had been decreasing in the past 53 years. Besides, crop water demand declined most significantly at the blossing and boll-forming stage, with change rate of -0.15 mm·a^-1. Furthermore, there were various multiscale cycle changes during the growth period. the water demand of crops in each growth period roughly changed as ‘high-low-high’ in the large periodic scale around 30 a and, as ‘low-high-low’ in the 15-17 a of the mesoscale cycle, but had no obvious cyclical characteristics on the interannual scale. Average crop water demands decreased roughly from west to east across North Xinjiang. The mutation results showed that the crop water demand decreased significantly in each growth period, especially in the northwest and southwest of North Xinjiang. In addition, cotton water demand was positively correlated with ave-rage wind speed, sunshine hours and average temperature during each growth period, and negatively correlated with relative humidity. The results would provide basic data for timely quantitative irrigation and improving water use efficiency of cotton in North Xinjiang.