Abstract: In recent years, the Bohai Sea and the Yellow Sea have shown the characteristics of decreasing dissolved oxygen concentration and leading to seasonal hypoxia, which will pose potential threats to coastal ecosystems. In this study, samples were collected from two cruises in summer (June 2011) and fall (November 2011) in Bohai and Yellow Seas, before and after the hypoxia and acidification events. For the ease of presentation, we defined the sampling periods as pre-oxygen decrease period and the post-oxygen decrease period, respectively. During the cruises, dissolved inorganic carbon (DIC), dissolved oxygen (DO) and dissolved inorganic nutrients were analyzed, and the controlling processes to the dynamics of carbonate parameters and nutrients were discussed. As a result: The photosynthesis and respiration are dominant factors controlling the changes of biogenic elements concentration in Bohai Sea during pre-oxygen and post-oxygen decreased period. In the Yellow Sea, the dominance of strong OM degradation in the Yellow Sea Cold Water in both cruises is primary reasons for the changes of nutrient and oxygen concentration.