Abstract: Some progresses of researches on ocean acidification in the Yellow Sea cold water mass were reviewed. Using the data of carbonate system obtained from monthly surveys in the North Yellow Sea in 2011, 2013 and 2017, it has been revealed that the net community calcification rate of the North Yellow Sea cold water mass is positively correlated to aragonite saturation state in the bottom water. A critical threshold between the net calcium carbonate precipitation and the net calcium carbonate dissolution in the North Yellow Sea cold water mass is the low aragonite saturation state value of 1.5–1.6. This is the first attempt to establish a semi-quantitative relationship between seawater carbonate chemistry parameters and the calcium carbonate process in China seas. The hydrochemical threshold between the net community calcium carbonate precipitation and the net community calcium carbonate dissolution determined in the North Yellow Sea is highly relevant to the upcoming China's ocean-acidification monitoring general project and the ecological effect assessment in the nearest future. Using this threshold value, and based on field measured data (including water temperature, salinity, dissolved oxygen and pH values at different depths) obtained by the North Sea Environmental Monitoring Center of the State Oceanic Administration (China) from 1977 to 2016 along a long-term seasonal surveying section on the west side of the North Yellow Sea, it has been convinced that seasonal acidification in the North Yellow Sea becomes serious since the end of the 20th century, as indicated by the autumnal mean aragonite saturation state of frequently below 1.5. The serious acidification status that threatens benthic shellfish (with an aragonite saturation state of lower than 1.5) and prolongs in both of summer and autumn only occurs after 2010. This change in aquatic chemistry is suggested to be partially responsible for scallop-culturing failures in the northwestern North Yellow Sea in the 2010s. Finally, this review paper highlights the urgent need to lay out disaster prevention and reduction measures in response to ocean acidification in some China seas.