In the estuarine area of the Changjiang River, the primary productivity is rather high, being 1,062mg C/(㎡?d) in average, and has a very large seasonal fluctuation range. It reaches maximum, 3,670. 2 mgC/(㎡?d), from June to September and decreases to 150mgC/(㎡?d) from April to May and October to November, 24.7mgc/ C/(㎡?d)in January. The annual average of the primary production is about 359.34gC/㎡.It increases gradually eastwards from the Changjiang Estuary to 123°30′E(the middle part of the investigated area), then decreases to the east boundary of the investigated area (124°00'E). Obviously, the runoff of the Changjiang River is the main factor for the dynamics of the primary productivity, and the upwelling of the Zhejiang Coast and the runoff of the Qiantang River cannot be neglected.