In order to evaluate the reliability of dual crop coefficient approach on calculating evapotranspiration of summer maize with mulched drip irrigation in arid region, the evapotranspiration of maize was measured by stable carbon isotope technique and water balance methods in measurement pits in 2016 and 2017. Five treatments were set up according to fixed irrigation cycle (W1, W2 and W3) and variable irrigation cycle (W4, W5) and the corresponding values were also calculated by dual crop coefficient approach. Experimental results showed that evapotranspiration calculated by dual crop coefficient approach had positive correlation with those values obtained by water balance methods, and the root mean square error was about 10mm. The crop transpiration calculated by dual crop coefficient approach also had positive correlation with those values obtained by stable carbon isotope technique, and the root mean square error was about 20mm. By calculation and analysis on the root mean square error, regression coefficient and consistency index, it can be concluded that dual crop coefficient approach was an effective method to calculate and distinguish evapotranspiration of summer maize with partial mulched drip irrigation in arid region. In whole growing season of summer maize, the simulated soil evaporation accounted for 21.33% and 23.97% of evapotranspiration and plant transpiration accounted for 78.67% and 76.03% of evapotranspiration in 2016 and 2017, respectively.