Abstract:The horizontal, vertical and sectional distribution of chloropyll a was studied in detail based on the data obtained by field observations from June to July, 2006 in the Yellow Sea and East China Sea. It was found that, the values of chloropyll a decreased from the shore to open sea in the horizontal distribution. Affected by Chang Jiang River and upwelling water, the high values were found at an area between 28°-32° N,122.5°-123° E. The condition of illumination and nutrients was the main factors of chlorophyll a distribution.