Evapotranspiration (ET), which is comprised of evaporation from soil surface (E) and transpiration from vegetation (T), plays an important role in maintaining global energy balance and regulating climate. Quantifying partitioning of ET is particularly important for accurate prediction of climate response to ecosystem carbon, water and energy budgets. Using eddy covariance measurements in maize fields for the growing season at the Experiment Station of Agro-ecosystem in Semiarid Area (ESASA) of Lanzhou University, we ran the revised Shuttleworth-Wallace model (S-W model), partitioned evapotranspiration in maize fields under plastic film mulch conditions into evaporation and transpiration, validated the performance of the model for different time scales and under different weather conditions with measured eddy covariance values, analyzed the driving factors, and determined parameter sensitivity of ET and its components. The results suggested that the simulated ET in the study area was in good agreement with the measurements in both sunny and cloudy days, but the model performed badly in rainy days. In diurnal timescale, the modified model performed well when ET was larger than 2 mm·d-1 in both sunny and mostly cloudy days, and the ratios of simulated values by S-W model to measured values were close to the 1∶1 line. But the model slightly overestimated ET in rainy days. Solar radiation and temperature were key environmental factors influencing ET in maize fields under plastic film mulch that led to seasonal variations. In general, T accounted for a small fraction of ET in maize fields under plastic film mulching. Diurnal variation in E/ET followed a single-peak curve, the low point was observed at night. At seasonal timescale, E/ET decreased from 18%to 8%at jointing stage, and kept at 8%level at tasseling stage and filling stage. We compared our result with others and found that both film mulch and environmental factors affected the value of E/ET. The E/ET was controlled by canopy stomatal conductance at diurnal timescale, while at seasonal timescale, it was mainly controlled by leaf area index (LAI) and soil moisture content (θ) which regulated transpired water from leaf stomata and evaporated water from bare soils. The sensitivity analysis showed that ET and its components were most sensitive to aerodynamic resistance from canopy to reference height (raa) and bulk resistance of boundary layer (rac), and moderately sensitive to bulk resistance of canopy stomatal (rsc), and insensitive to aerodynamic resistance from soil to canopy (ras) and soil surface resistance (rss). It was suggested that ET and its components were more sensitive to parameters related to canopy. Therefore, it was much more important to determine resistance parameters of raa, rac and rsc when simulating ET in maize fields under plastic film mulch using S-W model.%蒸散发(ET)包括植物蒸腾(T)和土壤蒸发(E)，在维持全球能量平衡和气候调节中起关键作用。量化蒸散发及其组分在准确预报气候对生态系统碳水通量和能量的响应中至关重要。基于兰州大学半干旱区农业生态系统试验站2014年玉米生长季涡度相关仪的观测结果，利用修订后的Shuttleworth-Wallace模型(S-W模型)对覆膜玉米田的蒸散发进行模拟，利用实测值对模拟结果进行验证，对蒸散发及其组分的影响因素和敏感性进行分析。结果表明： S-W模型对覆膜玉米农田蒸散发的模拟结果在日蒸散量大于2 mm·d-1的晴天和时晴时云天气较好，阴雨天气模拟结果较差，且模型模拟结果较涡度相关的实测值偏高。E/ET 在一天内的变化为单峰曲线，在生长季尺度上，在玉米快速生长期呈下降趋势，在之后的时间基本保持不变。覆膜玉米农田的E/ET在日时间尺度的变化主要受气孔导度影响，在生长季尺度主要受叶面积指数和土壤含水量的共同影响。敏感性分析表明，蒸散发及其组分对作物冠层高度与参考高度间的空气动力阻力(raa)和冠层内边界层阻力(rac)均较敏感，对作物冠层阻力(rsc)敏感性适中，对地面与冠层间的空气动力阻力(ras)和下垫面裸土表面阻力(rss)不敏感，在应用S-W模型模拟覆膜玉米农田蒸散量时，要特别注意阻力参数raa、rac和rsc的合理确定。
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