A review was made on the main environmental characteristics such as currents and water body, diluted water and its turning direction, upwelling, front, nutrients and its sources and plankton community in the Changjiang River estuary and its adjacent sea areas which could affect the growth, migration, assembling, resting and competition of harmful algae to form red tides. Analyses were also conducted to reveal features of the red tides events recorded in this area in terms of time, location and causative species. Some preliminary results from recent cruises carried out in the investigated sea area, where red tides were frequently occurring, were introduced.