Based on the data gained from three cruises in frequent Harmful Algae Bloom (HAB)occurrence areas in East China Sea during March and June, 2005, surface distributions of nutrient structures were analyzed. Results showed that in the prophase of diatom bloom, DIN/P and Si/P both showed descending trend from inshore to offshore area, but DIN/Si has a uniform distribution;When diatom bloom decayed and dinoflagellate bloom flourished, DIN/P, DIN/Si and Si/P showed a high level area in 28-30ºN. When dinoflagellate bloom decayed, DIN/P and Si/P showed an increasing trend from south to north,but DIN/Si showed decreasing trend from inshore to offshore area.Another result showed that lower DIN/P or higher concentration of PO
-P were propitious to the growth of diatom, while higher DIN/P or lower concentration of DIN were propitious to the growth of dinoflagellate. Lower DIN/Si or higher concentration of SiO
-Si will help diatom to gain an advantage over dinoflagellate in growth.