In order to explore the effect of thermal stratification on the vertical distribution of dissolved oxygen in Danjiangkou Reservoir, this paper selected the measured monthly vertical water temperature and dissolved oxygen concentration in 13 sections of the Danjiangkou Reservoir in 2023. Influencing factors of the vertical distribution of dissolved oxygen during thermal stratification and the reasons for the formation of anoxic zones were analyzed based on the dissolved oxygen demand side. Results showed that there was significant thermal stratification in Danjiangkou Reservoir from May to October. Thermal stratification in the reservoir mainly occurred at 5.00-10.00 m of surface water. Some sections in Hanjiang Reservoir area had a second thermocline in the middle layer of the water. Thermal stratification was the main reason for the formation of the dissolved oxygen stratification structure. The dissolved oxygen stratification of the surface water generally began to appear in July with the development of the thermal stratification. The thermocline in the middle layer of the water formed dissolved oxygen stratification in May. The location and changing trend of dissolved oxygen stratification were highly similar to thermal stratification. At the end of thermal stratification, the dissolved oxygen stratification structure receded with thermal stratification. Anoxic zones appeared in the periphery of Danjiang Reservoir and in the middle and lower reaches of Hanjiang Reservoir. Due to the long-term existence of thermal stratification and the stable stratification, the dissolved oxygen supplementation in the lower layers of the water had been limited for a long time, plus the oxygen consumption of the water, the bottom water began to form anoxic zones from August to October. In November, the vertical mixing was completed and the anoxic zone disappeared. This study revealed that the thermal stratification of the reservoir strongly drives the vertical distribution of dissolved oxygen in Danjiangkou Reservoir, which is important for a deep understanding of the water quality evolution and ecological succession process of Danjiangkou Reservoir.