To intensively characterize the spatial anomalies of ET0 change nationwide, it is necessary to make a reasonable partition to the whole country. Traditionally, the whole China is always divided into eight climatic regions according to the latitude and longitude, and the climate regions are roughly coincide with the socioeconomic division1323. However, there may be some uncertainty in sub-region selection based on visual inspection of the geographical distribution or administrative practices due to its vulnerability to subjective discretion9. This is especially true for the study of ET0 changing patterns due to the fact that ET0 involve in multifarious factors including geomorphologic features, topography factors and climate conditions. Therefore, the rotated empirical orthogonal function (REOF) method, a widely used clustering algorithm to objectively capture realistic spatial information, is employed in the current study to identify the homogenous regions regarding ET0 in the whole China. The first 11 EOFs together explain 80.8% of the variance and the first 8 EOFs together can explain 73.7% of the variance. The fact that more than 70% of the total variability is captured in the first 8 EOFs indicates that the complexity of spatial patterns of ET0 all over the country can mostly be explained by a small number of spatial structures. The percentages of variance of the new set of REOF modes generated by rotating the first eight loading vectors of the initial EOFs (Table S1) and correspondent isolines of the loading factor values (Figure S1) suggest that Mainland China can be categorized into eight homogenous regions (Fig. 1) by REOF analysis based on the annual ET0 series from 602 stations for 1961–2011. Eight leading modes deduced sub-regions can roughly be described respectively as following: East Center China (EC), Southeast China (SE), Southwest China (SW), Tibet Plateau (TP), North Center China (NC), Northwest China (NW), North China Plain (NP), and Northeast China (NE). In term of the regional average series of these eight homogenous regions, investigation on temporal patterns and their attributions across the whole China are presented in following sections.