Using the daily meteorological data from 54 stations in Xinjiang from 1963 to 2012, the water requirements of cotton (WRC) during the whole growing period and at different growth stages were calculated based on the FAO Penman-Monteith model and crop coefficient method. In addition, we used the methods of linear regression, Mann-Kendall test, and inverse distance weighting to analyze the spatio-temporal changes in WRC in Xinjiang in the last 50 years. The results show the following: 1) The average WRC during the whole growing period in Xinxiang was 759 mm. The values of WRC obtained from 54 meteorological stations in Xinxiang ranged between 555 mm and 1205 mm. The overall spatial distribution of WRC in Xinxiang varied obviously. The WRC in the south-east, south, and east was greater than that in the north-west, north, and west, respectively. 2) The WRC during the early growth and developmental stages of cotton in Xinxiang from 1963 to 2012 was assumed to be zonal and increased from north to south. During the middle and end growth stage, the WRC in the east was greater than that in the west. 3) The WRC at different growth stages showed a decreasing trend in the past 50 years, with the middle growth stage showing a more obvious downward trend. The greatest decline of 6.1 mm/10 years was observed in the middle growth stage, followed by 2 mm/10 years during the developmental stage and 1.3 mm/10 years in the end growth stage. The smallest decline of 0.6 mm/10 years was detected in the initial stage. 4) The WRC of the whole growing period in Xinxiang was overall reduced from 1963 to 2012. The average decline was 5.26 mm/10 years and the mutation of decline in Xinxiang began in 1981. (5) The spatial distribution of the decline in the average annual water requirement was similar to the average water requirement during the whole growing period. Generally, the spatial distribution of water requirement in Xinxiang was ascending from north-west to south-east.