Based on the annual and monthly average water temperature data of five hydrological stations, a comprehensive and systematic analysis was conducted on the annual and interannual variation time series of water temperature using mathematical statistics and complex Morlet wavelet functions in the Hanjiang mid-lower reaches river. This study quantitatively evaluated the degree of changes in downstream river water temperature since the construction and elevation of the Danjiangkou Reservoir, revealing the complex structure of water temperature changes at multiple time scales. At the same time, the characteristics of water temperature during the periods of water bloom susceptibility and fish spawning were analyzed. The results show : (1) The degree of change in water temperature is related to distance. Under the influence of low-temperature water discharge from the reservoir, the characteristic values of Huangjiagang hydrological station under Danjiangkou Dam have significantly changed, with an average annual temperature showing a downward trend. Xiangyang station, 109km away from the dam, is affected to some extent in summer and winter. The water temperature of the river below Huangzhuang has recovered to its natural state under the influence of the climate along the way. (2) The annual water temperature at Huangjiagang station exhibits periodic changes on time scales of 25-28 years, 15-19 years, and 9-11 years. The scale characteristics vary in different periods, and the phased characteristics of water temperature changes are obvious; The main periods of annual water temperature at Xiangyang, Huangzhuang, and Xiantao stations are concentrated at the 5-7 year and 9-11 year scales, which is consistent with the characteristic scale of periodic changes in the natural water temperature sequence of Huangjiagang station. (3) After the Danjiangkou Dam was raised, the water temperature from below the dam to Xiangyang further delayed, and the daily average water temperature at Xiangyang station reached 18 ℃ with a delay of about 20 days; The increase in water temperature during the period of water bloom susceptibility from January to March ranges from 0.9 to 1.5 ℃, and the increase in temperature will to some extent increase the frequency of water bloom outbreaks.