Crop water requirements are crucial for agricultural water management and redistribution. Based on meteorological and agricultural observation data, the effective precipitation (Pe), water requirements (ETc), and irrigation water requirements (Ir) in the maize growing areas of Inner Mongolia were calculated. Furthermore, climatic trends of these variables were analysed to reveal their temporal and spatial distributions. The research results are as follows: the average Pe of maize in Inner Mongolia during the entire growth period was 125.9 mm, with an increasing trend from west to east. The Pe in the middle growth period of maize was the highest and was small in the early and late growth stages. The Pe climate exhibited a negative slope with a decreasing trend. The average ETc of maize during the entire growth period was 480.6 mm. The high-value areas are mainly distributed in the Wulatzhongqi and Linhe areas. The average Ir of maize during the entire growth period was 402.9 mm, and the spatial distribution is similar to that of ETc. In each growth period, Ir showed an increasing trend. Supplemental irrigation should be added appropriately during each growth period to ensure the normal growth of maize. This study can provide an effective basis for the optimisation of irrigation and regional water conservation in the maize cultivation area of Inner Mongolia
