Abstract: Suspended particles in the West Pacific surface water were collected during the KX08-973 Cruise(Nov.14,2008~Jan.19,2009). Four kinds of phytoplankton lipids biomarkers, i.e. Brassicasterol,Dinosterol,C37-Alkenone,and 1,15-C30 alkyl-diol, corresponding to diatoms,dinoflagellates,coccolithophores,and Eustigmatophytes algae were collected by organic geochemistry method. The variability and influencing factors of the phytoplankton biomass and communities structure were studied according to their distribution. The results show that the obtained biomass are correlated well with the Chl-a,indicating the validation of biomarker lipids to the reconstruction of the ocean productivity. The biomass distribution has distinct regional differentiation, highest in Yangtze River estuary and related shelf areas,followed by the area off eastern New Guinea and the zone off eastern Philippines,with the lowest in the pelagic. Fluvial transport,ocean currents, regional landform configurations and resuspension of the shelf sediment are the main factors effecting the phytoplanktons biomass distribution. As the result of competition for nutrient,the phytoplanktons biomass is dominated by diatom,with dinoflagellate,coccolithophores and Eustigmatophytes as minor contributors. The data obtained from the present research can be applied not only to modern marine ecological investigation,but also for paleoceanographic reconstruction.