Abstract: This paper represents the results of an investigation on algal succession and the occurring trend of waterblooms in Xiangxi Bay fromJanuary 2003 to December 2004. The results were discussed in four periods. The first period was from January2003 to June 2003, the second was fromJuly 2003 to December 2003, the third was fromJanuary 2004 to June 2004, and thefourth was fromJuly 2004 to December 2004, each period was 6 months. A total of 115 species of algae belonging to 7 phyla and 85 genera was observed when the Three Gorges Reservoir had been sluiced for half a year. The species number of each phylumwere as follows:Bacillariophyta 22, Chlorophyta 67, Cyanophyta 12, Pyrrophyta 4, Euglenophyta 5, Cryptophyta 2, Xanthophyta 3. The results showed that the species richness of green algae increased notably in the second period. It was almost 3 times ofthat before sluice, and then went down slowly in the third and the fourth period. The species richness of diatoms represented atrend of decrease. Other phyla varied slightly. The peak value of cell density and biomass of algae were both noted at the S6 station with the highest cell numbers of 6193 ?07cells/L (June) and the most biomass of 87124mg/L (March). The minimal values were almost noted at the S1 station except in March. According to the investigated results, the authors give a forecast analysis on the trend of waterblooms occurring in the Xiangxi Bay. We predict that the occurring odds of waterblooms is small in themain channel, and the waterblooms are easy to occur in distributaries and some lentic areas, especially in spring when the watertemperature rises gradually and sunlight becomes abundant.