Abstract:Evapotranspiration (ET) of maize plant during the developmental stages was measured with electronic weighing lysimeters. The results show that the crop ET varied with watering conditions and reached its maximum in the blooming-grouting period. The ratio ground evaporation to maize transpiration is 1:4. Influence of field micro-climate to crop ET is comprehensive, and solar radiation plays a leading role. Stomatal diffusion resistance is negative correlateff with the rate of crop ET . Leaf water potential decreases along with the acceleration of crop ET. Our preliminary conclusion is that stomatal diffusion resistance and leaf water potential would be the two important parameters of soil-plant-atmospheric water circulation.