Evapotranspiration in five major forest ecosystems in Yunnan was measured using eddy covariance from 2003 to 2015. The characteristic and variation of evapotranspiration were compared, and the relationship between evapotranspiration and soil water content as well as precipitation was analyzed in the present study. The results showed that the dynamic patterns of diurnal evapotranspiration of five forest ecosystems were all characterized by a single-peak curve, but the occurrence of peaking time and the patterns in diurnal evapotranspiration were not consistent. Both daily and monthly evapotranspiration among five forest ecosystems followed an unimodal curve form. Maximum evapotranspiration rate was observed during July and minimum during January. Likewise, the seasonal evapotranspiration was characterized by the highest evapotranspiration during rainy season and lowest during the dry season. The multi-year mean annual evapotranspiration (the percentage of evapotranspiration to precipitation) of the tropical rainforest, rubber plantation, savanna, subtropical evergreen broad-leaved forest, and subalpine coniferous forest was 795.68 mm (55.05%), 774.54 mm (59.77%), 435.35 mm (56.58%), 767.69 mm (52.80%), and 438.83 mm (42.17%), respectively. It implied that the moisture of those forest ecosystems is sufficient. The relationship between evapotranspiration and soil water content was not the same over different forest ecosystems, which showed that the water-use strategies were varied among different forest ecosystems. The results provided a scientific basis for the assessment of ecological hydrological effects and water-use strategies of forest ecosystems, and the understanding of the responses to climate changes.