Frequent harmful algal blooms in coastal waters of China in recent years have been believed to be the result of eutrophication. However, in the southern Yellow Sea, the historical process of water eutrophication is not clear for lack of survey data. Focusing on this problem, we examined the clues of marine environmental changes preserved in sediment cores. With the use of ~(210)Pb and biogenic silica (BSi), we estimated the age of sediment and rebuilt the change trend of paleo-productivity. The historical process of eutrophication in the past 100a in coastal waters of the area is discussed. Results revealed obviously the variation in primary productivity in the past 100a. Results show that before 1980s, primary productivity was relatively low in the study area, and its decadal fluctuation was closely related to dry/wet climate changes in North China. However, after 1980s, primary productivity increased significantly by 31%254%, which obviously departed from the regulation of natural climate changes. This sudden increase clearly indicates that eutrophication has become serious, for which the massive emission of terrestrial nitrogenous contaminants to coastal waters is responsible, under the rapid development of Chinese economy.