An extensive investigation on the main tributaries of the Three Gorges Reservoir (TGR) region was conducted in autumn (Oct. 2015), with focuses on riverine CO2 partial pressure (pCO2) and its associated controls. Our results indicated that pCO2 in the main rivers of the TGR region ranged from 18.75 to 296.31 Pa, with a mean value of (141.06±77.51) Pa in the autumn, which was much higher than the atmospheric CO2 concentration. Therefore, the studied rivers acted as an atmospheric CO2 source, and the mean CO2 emission rate to the atmosphere was estimated at (101.1±78.0) mmol·(m2·d)-1. The highest and lowest values were (131.9±101.8) and (70.3±54.3) mmol·(m2·d)-1, respectively. pCO2 in the main rivers of the TGR area was significantly related to DO, pH, and bicarbonate. Furthermore, the biogeochemical process of within-river respiration of organic carbon rather than photosynthesis resulted in negative relationships between pCO2 and DO or pH because of the high velocities and short residence time in these mountainous rivers and streams. Our results will help to accurately develop the carbon budget for the rivers of the Three Gorges Region.