Abstract: hekou harbour is located at the north side of Shenzhen Bay,and its eutrophication is becoming serious in recent years. The Chla and Chlb contents of phytoplankton and N,P levels of sea water at 4 typical tides are examined continuously for 24 hours,and the relationship between phyto-plankton growth and N,P levels are revealed.There are red-tide algae existing in the sea water and Bacillariophyta is the dominant component.