Abstract: To explore the impacts of flooding duration on the functional diversity of plants in the drawdown zone of large reservoirs, this study selected three large reservoirs in the southwestern region as the research areas. Through systematic measurement of the functional traits and functional diversity indicators of plants in the floodplain under different flooding durations. The results showed that: 1）A total of 34 species of vascular plants were recorded, belonging to 30 genera and 17 families, and a total of eight dominant species with a coverage ≥ 25% were recorded. 2）The moderately flooded area (MF) exhibits the highest functional diversity, which was significantly higher than those of the slightly flooded area (SF) and the severely flooded area (LF). The trait differentiation and ecological niche differentiation of the dominant species are significant. 3）The functional homogeneity in the LF zone was significantly reduced, and the diversity indices of each function decreased significantly. Only the main root diameter significantly increased (63% higher than the MF zone, and 154% higher than the SF zone), indicating that under strong waterlogging stress, the community constructed a redundant functional structure by specifically thickening the main roots. Cynodon dactylon was a highly specialized key species in these zones. 4）The community coverage, stem branch number, root length and total root fresh weight in the SF area were significantly higher than those in the MF and LF areas. This indicates that mild flooding mainly selects for trait combinations with rapid colonization ability. In this area, the traits of Cynodon dactylon, Eleusine indica, Ageratum conyzoides and Xanthium sibiricum are spatially dispersed and independent. 5）The CV value of leaf traits remains relatively large across the waterlogging gradient, confirming their sensitivity. Overall, in the southwestern reservoir drawdown zone, the duration of flooding is the key driving factor regulating the degree of functional trait dispersion and functional diversity. For the LF area with an average annual flooding duration of ≥ 180 days, a strategy of functional redundancy is adopted; for the area with an average annual flooding duration of < 180 days, a strategy of functional complementarity is adopted. This difference in functional diversity response based on the flooding gradient drives the formation of the multi-adaptive strategies of dominant species. It is suggested to implement differentiated community construction strategies based on the duration of flooding.