Abstract: Primary production supports substantial biomass and higher trophic level organisms in the coastal waters, but the mechanisms regulating primary production in coastal waters are still difficult to assess. In this study, primary production in the Yellow Sea and the East China Sea was measured via ¹⁴C tracer in summer 2006 to reveal their distribution features and the impact factors. Our results showed that the depthintegrated primary production ranged from 378.65 to 6 403.47 mg/(m²·d) with an average of 2 059.56 mg/(m²·d). The distribution of primary production indicated that (1) primary production in the East China Sea was higher than those in the Yellow Sea; (2) primary production in sea areas influenced by the Kuroshio waters was significantly lower than those in the shelf regions; and (3) high primary production was observed in the southeastern region of Changjiang estuary and the southwestern region of Jelu Island. The relationship between primary production and environmental factors suggested that high primary production mostly occurred in seawaters with temperature of 21-26 ℃, and the primary production was regulated by the availability of nutrients and lights. The low primary production in the regions influenced by the Kuroshio waters was ascribed to the low nutrients, and the high primary production in the southeastern region of Changjiang estuary and the southwestern region of Jelu Island was ascribed to the abundant nutrients supplied by the Changjiang river and the cold eddy.