Abstract: The scientific assessment of the distribution and mechanism of seawater partial pressure of carbon dioxide (pCO₂) in the coastal sea is important for evaluating the air-sea CO₂ exchange flux over China seas and achieving the goal of “carbon neutrality”. In this study, we investigated the distribution, controlling factors, and air-sea CO₂ exchange flux in the Bohai Sea using the underway data from the summer of 2014 and 2021. The results showed that (1) the Bohai Sea pCO₂ ranged from 270 to 1060 μatm in August 2014, and the high values occurred in the Liaodong Bay, Bohai Bay, and Laizhou Bay; while pCO₂ in the central region of the Bohai Sea ranged from 313 to 697 μatm in August 2021, and the high values occurred near the Bohai Strait and the Yellow River estuary. (2) Based on the Pearson correlation analysis, biological activity was the main factor affecting the distribution of pCO₂ in the Bohai Sea in summer, and freshwater input from high pCO₂ rivers led to a high background value of pCO₂ in the Bohai Sea; the enhanced biological photosynthesis led to a decrease in pCO₂ in the central region of the Bohai Sea as the offshore distance increases. (3) The Bohai Sea was a source of atmospheric CO₂ in summer; there were differences in the air-sea CO₂ exchange flux between different regions; that was, the air-sea CO₂ exchange flux in the Laizhou Bay was higher than Liaodong Bay and Laizhou Bay, while the central Bohai Sea had the lowest air-sea CO₂ exchange flux.