To investigate the impact of damming on CO₂ partial pressure and CO₂ release from water-air interface in tail tributary of the Three Gorges Reservoir during low water level period, the Yulin River, one of the dam-building tail tributaries of Three Gorges Reservoir was sampled in August 2019. The key physical and chemical environmental factors were measured in situ, the CO₂ partial pressure (p_CO2) and water-air interface diffusion flux (Flux(CO₂)) were calculated by headspace equilibrium method combined with Henry's law and thin boundary layer theory. The results show that the surface water p_CO2 of the Yulin River during low water level period is 54.55~336.73 Pa, with an average of 206.68 Pa, the Flux(CO₂) is 1.65~67.84 mmol/(m²·d), with an average of 39.01 mmol/(m²·d), which is the source of atmospheric CO₂ emission. The emission level of CO₂ from the Yulin River is significantly higher than that of the tributaries in the middle and lower reaches of the Three Gorges Reservoir area. The near reach of the upstream of the dam is lake-type's water (velocity <0.05 m/s), while the far reach of the upstream and downstream are transition-type's water (velocity:0.05~0.2 m/s). The p_CO2 and Flux(CO₂) of lake-type's water are significantly lower than that of transition-type's water, and p_CO2 increases rapidly with the increase of water depth. Correlation analysis and multiple stepwise regression analysis show that p_CO2 and Flux(CO₂) in the Yulin River during low water level period were significantly affected by physical and chemical environmental indexes such as water temperature, pH, DO and Chl-a, and Chl-a is the most important factor affecting p_CO2, while p_CO2 is the most important factor affecting Flux(CO₂).