Partitioning evapotranspiration (ET) into evaporation (E) and transpiration (T) is essential for understanding the global hydrological cycle and improving water resource management. However, ET partitioning in various ecosystems is challenging as some assumptions are restricted to certain areas or plant types. Here, we developed a novel ET partitioning method coupling definitions of leaf and ecosystem water use efficiencies (WUEleaf and WUEeco, respectively). We used 25 eddy covariance flux sites for 196 site-years to evaluate T:ET characteristics of seven plant functional types (PFTs) at different spatiotemporal scales. The results indicated the spatiotemporal characteristics of WUEleaf and WUEeco were not consistent, resulting in T:ET variation in the seven PFTs. Deciduous broadleaf forests had the highest mean annual T:ET (0.67), followed by evergreen broadleaf forests (0.63), grasslands (0.52), evergreen needleleaf forests (0.46), and woody savanna (0.41), and C3 croplands had higher T:ET (0.65) than C4 croplands (0.48). The annual mean leaf area index (LAI) explained about 26% of the variation in T:ET, with the trend in T:ET consistent with the known effects of LAI. The overall trends and magnitude of T:ET in this study were similar to different results of ET partitioning methods globally. Importantly, this method improved T:ET estimation accuracy in vegetation-sparse and water-limited areas. Our novel ET partitioning method is suitable for estimating T:ET at various spatiotemporal scales and provides insight into the conversion of WUE at different scales.