Abstract: By using multiple regression equation of the interpolation method, corn growth stage average precipitation spatial distribution was calculated in calendar year, the absolute error, inverse distance weighting method is used for error correction. On the basis of the water demand and the sensitivity index of lack rain in each stage of maize, the influence degree by precipitation was calculated in each growth stage. Using the proportion of water demand in each stage accounted for the whole growth period as the weight, It obtained the effects result of the precipitation in whole growth period. Inner Mongolia region precipitation generally difficult to meet the maize growth needs, and gradually reduce from east to west.