To understand the variation patterns of water temperature in the Xiluodu Reservoir area after the impoundment and operation of the Wudongde and Baihetan reservoirs, this study analyzed the spatiotemporal variation characteristics of water temperature and the evolution process of thermal stratification in the Xiluodu Reservoir area based on in-situ water temperature observation data from 2019 to 2024 and historical hydrological data from 2014 to 2018. The analysis was conducted using mathematical statistics, comparative analysis, and the Mann-Kendall trend analysis method, incorporating thermal stratification evaluation indices. The results show that after the impoundment of the upstream cascade reservoirs, the thermal stratification stability gradually increased. Downstream water temperature exhibited a flattening trend, characterized by higher values in autumn and winter and lower values in spring and summer, and the occurrence of low water temperatures showed a lagging characteristic. Furthermore, the degree of water temperature flattening and lagging increased with the number of cascade reservoirs. The peak value of the thermal stratification stability index increased from 2.52 m^-1 to 3.71 m^-1, while the vertical temperature gradient decreased year by year after impoundment. The mean inflow water temperature decreased by 0.52°C in summer and increased by 2.64°C in winter, with the annual temperature range decreasing by 7.78%. The mean outflow water temperature decreased by 0.53°C in summer and increased by 1.93°C in winter, with the intra-annual extreme variation range decreasing by 0.6% to 11.1%. The occurrence time of the minimum water temperature at various cross-sections along the channel was delayed by 4 to 26 days compared with the pre-impoundment period.