Due to the importance and complexity of crop evapotranspiration estimation under drought stress, maize drought stress special experiment was conducted based on six large-scale weighing lysimeters at Xinmaqiao Irrigation Experimental Station, the empirical parameters a and b of the Angstrom formula were optimized based on the measured solar radiation data from the experimental station, and the calculation results of the reference crop evapotranspiration were optimized, and then the characteristics of maize evapotranspiration under different drought stress scenarios were analyzed, moreover the maize evapotranspiration under drought stress was estimated by using basic crop coefficients, including Kcbini，Kcbmid, and Kcbend and upper limit of crop coefficient Kcmax, which were calibrated by genetic algorithm in the process of estimating maize evapotranspiration under no drought stress based on dual crop coefficient approach. The results showed that early mild water deficit may stimulate the adaptability function of maize, and normal physiological function of that would return after re-watering;water deficit would not only decrease current evapotranspiration of maize, but also generate the cumulative effect, which transferred stress influence to later growth stages;the same drought stress intensity had a more obvious effect on the reproductive growth stage of maize, and it may cause permanent stress;the calibration results of Kcbini, Kcbmid, Kcbend and Kcmax were 0.150, 1.090, 0.152 and 1.400, respectively, and the root mean square error (RMSE) and mean absolute error (MAE) of estimated evapotranspiration results under no drought stress in whole growth period using these crop coefficients were 1.39mm and 0.97mm, respectively, which were 6.74% and 8.23% less than those of estimated results based on FAO-56 recommended approach, the means of RMSE, MAE and MRE of estimated evapotranspiration results under two different drought stress scenarios were 1.60mm, 1.18mm and 6.73%, respectively. Therefore, the estimation of maize evapotranspiration under drought stress based on dual crop coefficient approach and genetic algorithm were reasonable and reliable, and this research would provide theoretical foundation for formulating suitable irrigation system and reducing risk of agricultural drought loss.