A process-based physiological model, EALCO (Ecological Assimilation of Land and Climate Observation), was used to simulate the evapotranspiration from maize cropping system and to investigate the responses of evapotranspirational processes to projected climate change. Measured evapotranspiration from the maize cropping system by an eddy covariance system was used to test the model′s performance. The results showed that EALCO has high capability to simulate the evapotranspiration in both hourly and daily scales, and explained 67% of daily evapotranspiration. By dividing the evapotranspiration into soil evaporation and canopy transpiration in growing season, simulated soil evaporation counted for 36% of evapotranspiration. Simulated evapotranspiration and canopy transpiration will increase due to the increase in air temperature, but soil evaporation tends to decrease. Simulated evapotranspiration was strongly sensitive to the decrease in precipitation, which mainly leads to the decrease in soil evaporation. The increase in atmospheric CO2 concentration will significantly decrease canopy transpiration. Under the scenarios of future climate change in 2100, the model suggested that the evapotranspiration during the growing season will decrease; however, the decreased evapotranspiration can not compensate the decease in precipitation. As a consequence, future climate change will increase the possibility of crop water stress, intensify the trends of warming and drying, and hence threaten crop production and ecological environment in the studied region.