The process of evapotranspiration (ET), which takes into account both evaporation (E) and plant transpiration (Tr), plays a prominent role in water and heat exchange in terrestrial ecosystem, given that it involves interactions between plants, soil and atmosphere. Evapotranspiration is also vital for developing water-saving irrigation schemes and improving the crop water productivity of farmland ecosystems. As for the components of evapotranspiration, investigating transpiration and evaporation separately can help us understanding crop water requirements more thoroughly. We investigated the variation in crop water consumption during the growing season for a maize field located in the Linze Inland River Basin Research Station of the Chinese Ecosystem Research Network. In this investigation, we obtained essential data, including microclimate, turbulent exchange, evaporation, and leaf stomatal conductance, in 2009. Based on these data, we simulated transpiration and evaporation in half-hour time steps using the Shuttleworth-Wallace (S-W) model. Comparing the calculated ET data with eddy covariance data through correlation analysis, we found that the correlation coefficient (R²) was 0.70, the mean square error (MSE) was 0.67, and P less than 0.001. A correlation analysis between evaporation data measured by a micro-lysimeter and evaporation data simulated by S-W model shows a good accordance between them, with R² of 0.64, MSE of 0.67, and P less than 0.001. The S-W model was found to be useful for dividing evapotranspiration into transpiration and evaporation. After applying the model, it can be concluded that during the growing season, the cumulative evapotranspiration was about 640 mm, which consisted of 467 mm of transpiration and 173 mm of evaporation. It means that transpiration and evaporation accounted for 72.9% and 27.1% of evapotranspiration, respectively. On a daily basis, transpiration ranged from 0 to 6.3 mm/d (mean = 2.8 mm/d), while evaporation ranged from 0 to 4.3 mm/d (mean = 1.0 mm/d). The ratio of transpiration to evaporation varied with crop growth. Transpiration (water consumption) of maize during different growing stages can be summarized as follows. The ratio of transpiration to evaporation (Tr/E) was 0.04 when the leaf area index (LAI) was close to zero from seeding to emergence stage, indicating that evaporation constituted a large proportion of evapotranspiration. From emergence to jointing stage (LAI= 0.35), the ratio of Tr to E was 0.8, while transpiration and evaporation accounted for 45% and 55% of evapotranspiration, respectively. However, from jointing to tasseling stage (LAI= 3.81), when most of the solar radiation was captured by the canopy, transpiration accounted for 87.4% and evaporation dropped to only 12.6% of evapotranspiration, while Tr/E was 7.0. From tasseling to filling stage, the ratio of Tr to E was 5.2, while transpiration and evaporation constituted 83.8% and 16.2% of evapotranspiration, respectively. Finally, from filling to maturity, the ratio of Tr to E dropped to 1.4 causing by little water requiring by mature maize. From these findings about evapotranspiration related to maize, it can be seen that water consumption varies by regions, growing stages of the crop, and water availability. Evapotranspiration was greatest during the tasseling and filling stages, and irrigation was also heavy at these times, indicating that the irrigation scheme was reasonable. The total evapotranspiration over the growing season was 640 mm, while the total water supply (the sum of irrigation and precipitation) was 895 mm, which means that the current irrigation scheme supplied a sufficient amount of water to the maize. However, as precipitation changes during the growth stage, the irrigation scheme should also be adjusted such that the water supplied is balanced with the water requirements of the crop for a particular growth stage. To keep water balance between supply and consumption will be help water saving in this area. Both meteorological factors and crop conditions can affect evapotranspiration. Microclimate changes with meteorological factors, leading the variation in total evapotranspiration. In addition, the earth surface coverage, canopy aerodynamics, and other conditions are affected by the crop itself (especially the LAI), which can alter the ratio of crop transpiration and water evaporation from soil.