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In order to understand evapotranspiration (ET) of rotation fields in the North China Plain, a typical wheat-maize rotation field at the Yucheng site in Shandong Province was chosen as a case study. The continuous daily flux and meteorological observation data at this site were systematically collected to investigate the changing characteristics of ET and environmental factors from 2003 to 2010. Also the boosted regression tree was used to identify the influencing factors of ET in different growing seasons. The results showed that the ET was ranged from 0mm/d to 9.6mm/d, and the peak value of ET in the wheat season was usually higher than that in the maize season. Moreover, annual total value of ET in the wheat season was obviously higher than that in the maize season. As for the non-growing season, ET during this period accounted for less than 4% of annual total ET. The net radiation was an important factor affecting the seasonal changes of ET in different stages in this field. Its relative contribution was in the decreasing order of wheat season (81.4%), maize season (52.7%), and non-growing season (36.8%). In addition to net radiation, the vapour pressure deficit had also a certain impact on ET in different growing seasons, and its relative contribution in the maize season (17.6%) was higher than that in the winter wheat season (5.9%). As for the non-growing season, the relative contribution of soil water content and wind speed was relatively higher, which were 22.5% and 17.0%, respectively. The research result can provide an important reference for formulating reasonable irrigation management and optimizing crop models under a changing environment.