Standing stock and production of phytoplankton in the northern South China Sea (nSCS) were studied during February 2006 when northeast monsoon strongly prevailed. The results clearly showed that the distributions of phytoplankton were closely related to the physical-chemical-biological coupled processes driven by the northeast monsoon. The chlorophyll-a (Chl a) concentration varied from 0.03 mg·m-3 to 1.21 mg·m-3 (the average value was (0.33±0.33) mg·m-3). The most of high values appeared in the coast areas near Guangdong Province and in the sea area to the east of Hainan Island. The lowest and highest value of primary production (PP) were 41.3 mgC·m-2·d-1 and 1040.0 mgC·m-2·d-1. The distribution patterns of Chl a differed from PP in three different regions. As for Chl a, coastal region ((0.53±0.50) mg·m-3) had much higher value than open sea ((0.31±0.30) mg m-3) and shelf region ((0.20±0.11) mg·m-3); as for PP, the variation showed opposite: open sea had the highest value ((631.3±578.0) mgC·m-2·d-1), followed by shelf (1622 mgC·m-2·d-1) and coastal region (41.3 mgC·m-2·d-1) in turn. Photosynthetic picoplankton was found to be the greatest contributor to phytoplankton stocks and production in all study area, especially in open sea, 47% and 66% respectively.