Abstract: Pan evaporation serves as an important indicator of evaporative capacity, and analyzing its spatiotemporal variation is essential for accurately estimating reservoir evaporation losses and understanding hydrological and climatic dynamics in reservoir regions.This study examines the spatiotemporal variability of D20 pan evaporation and its climatic drivers using data from 25 meteorological stations distributed along the Three Gorges Reservoir and its upstream cascade reservoirs from 1980 to 2019.The findings reveal significant regional differences in pan evaporation, demarcated by the 103.5°E and 108.5°E longitudes.The western region (4 stations) exhibited the highest annual average evaporation (2 457 mm), with pronounced seasonal variation—peaking in spring (993 mm) and reaching a minimum in autumn.Their interannual trends show a marked decline before 1999, followed by an upward trend.The central region (15 stations) recorded the lowest annual average evaporation (1 105 mm), while the eastern region (6 stations) had intermediate values (1 382 mm).Both the central and eastern regions demonstrated a summer peak and winter trough, with the central region notably experiencing a distinct minimum in June.In the estimation of evaporation losses from the Three Gorges Reservoir and its upstream cascade reservoirs, it is necessary to pay attention to the differences in pan evaporation in three regions, with a particular focus on the evaporation losses of reservoirs in the western region.The differences in pan evaporation in the three regions are related to the spatial pattern of the monsoon circulation′s influence.When analyzing the hydroclimatic change patterns in different regions, it is important to consider the differences in climate drivers such as atmospheric circulation.