To investigate the impact of dam construction on CO2 partial pressure and CO2 water-air interface release of rivers in summer, the Yulin River, one of the dam-building tributaries in the end of Three Gorges Reservoir was sampled in August 2019. The key physical and chemical environmental factors were measured in situ, the CO2 partial pressure (pCO2) 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 pCO2 of the Yulin River in summer is 54.55 ~ 336.73 Pa, with an average of 206.68 Pa, the Flux(CO2) is 1.65 ~ 67.84 mmol.(m².d)^-1, with an average of 39.01 mmol.(m².d)^-1, which is the source of atmospheric CO2 emission. The emission level of CO2 from Yulin River is significantly higher than that of the tributaries in the middle and lower reaches of the Three Gorges Reservoir area. In summer, the Yulin River is greatly affected by dam construction. The near reach of the upstream of the dam is lake-type"s water (velocity < 0.05 m.s^-1), while the far reach of the upstream and downstream are transition-type"s water (velocity: 0.05 ~ 0.2 m.s^-1). The pCO2 and Flux(CO2) of lake-type"s water are significantly lower than that of transition-type"s water, and pCO2 increases rapidly with the increase of water depth. Correlation analysis and multiple stepwise regression analysis show that pCO2 and Flux(CO2) in the Yulin River in summer 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 pCO2, while pCO2 is the most important factor affecting Flux(CO2).