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.