Water scarcity is the primary limiting factor in crop production in vast north-western China. Crop water requirement depends mainly on the nature and stage of growth of the crop and environmental conditions. To assess the relationship of water conditions and crop production, we analyzed the water adequacy level and production in maize during the entire growth stages in the Loess Plateau in Gansu province. Maize phonological data and corresponding meteorological data covering the period between 1981 and 2008 were collected in the Tianshui and Xifeng Agrometeorological Experimental Stations. Based on these data, water requirement of maize during all developmental stages was analyzed by using crop coefficient and the FAO Penman-Monteith formula. A model was generated. The results indicated that water supply was generally adequate for maize growth in Gansu Loess Plateau, with an annual mean water adequacy index (WAI) higher than 0.50. The WAI in Longdong (Xifeng) and Longxi Loess Plateau (Tianshui) showed a correlative relationship, exhibiting a similar trend in variation over the last 28 years. Historically, the year of 1995 was a turnning point in WAI. From 1981 to 1995, the WAI was decreased by 0.12 every ten years in Longxi Loess Plateau and 0.11 in Longdong Loess Plateau. However, from 1995 to 2008, it was increased by 0.18 per 10 years in Longxi Loess Plateau and 0.06 in Longdong Loess Plateau. Among the various growth stages of maize, WAI was at its best during the maturation stage; suboptimal during the early growth stage, and poor during the fast growth stage. Air precipitation satisfied more than 70% of the water requirement of maize during maturation stage, whereas only about 49%-55% of the requirement during the fast growth stage. WAI during stages of germination to seven leaves, jointing to tasseling, tasseling to milky maturation, and milky maturation to full maturation remained high in the 1980s, low in 1990s and returned high in the early 2000s. WAI in the period of seven leaves to jointing stayed continuously low from 1980s to the beginning of the 21st century. Geographically, WAI in Longxi Loess Plateau was higher by 0.1 than that in Longdong Loess Plateau. The water requirement of maize in Longxi Loess Plateau was higher than Longdong Loess Plateau in all growth stages except the maturation stage. The correlation between maize climate yield and the WAI was most significant in seven-leaf to jointing stage, followed by jointing to heading stage, suggesting that these two stages are critical in water requirement. Such a correlation was notable in jointing to tasseling stage, but it was non-significant in stages of germination to seven leaves, tasseling to milky maturation, and milky maturation to maturation. This model on WAI and maize growth/production can be used to evaluate the suitability for maize growing in areas in Gansu Loess Plateau and provide scientific basis for crop management for higher yields.