Abstract: Using film and straw mulch and different irrigation methods, an experiment was conducted to determine evapotranspiration from spring maize land. Large-scale weighing lysimeter and miniature evaporator were used to measure evapotranspiration, which combined with weather, leaf area, yield data and other auxiliary data were used to compare the advantage of different mulch and irrigation methods. The measured data were analyzed to learn pulse relations between rainfall, irrigation with soil evaporation, and stage effect of rainfall on total and reference crop evapotranspiration. It is indicated that proportion of soil evaporation to evapotranspiration shows “high-low-high” changing rule at different growth stages. Straw mulch presents better effect on reducing invalid evapotranspiration than film mulch. The relation between evapotranspiration and leaf area index of different treatments is better with a much linear functional relationship. Trough the relationship model, crop coefficients for different growth stages of spring maize and water use efficiency for the entire growth period are determined. The experimental results indicate that deficient irrigation has little effect on water use efficiency in arid Hexi region. The effectiveness of deficient irrigation is better in spring maize with film mulch than with straw mulch.