Lake Taiping is one of the national key protected lakes, but its ecological baseline information is lacking. A preliminary study was conducted on the phytoplankton community structure in Lake Taiping from September 2012 to March 2013. A total of 126 phytoplankton species belonging to 7 phyla, 93 genera were identified. The phytoplankton community was dominated by Chlorophyta, which is comprised of 40 genera and 68 species. The average phytoplankton cell density was 127.12×10⁴ cells/L, in which Cyanophyta and Chlorophyta cells accounted for 61.5% of the total cell density. The average phytoplankton biomass is 0.74 mg/L and 40.3% of them was Cyanophyta and Chlorophyta. There were a number of dominant planktonic species in Lake Taiping but none of them absolutely dominated. The number of indicator species of alpha and beta pollution is 9 and 28, accounting for 7.1% and 22.2% of the total number of the species in the lake, respectively. The averages of Shannon-Wiener, Margalef index and Pielou evenness index at every sampling station were 2.48, 2.35 and 0.71, respectively. The indexes of phytoplankton evaluation of Lake Taiping were not consistent, but all the indexes water quality indexes were relatively consistent, indicating that the experienced β-α-moderate pollution. Compared to previous reports, phytoplankton species composition in Lake Taiping did not change significantly. Cell density and biomass showed an increasing trend. Besides, the indicator species of clean-water have disappeared. More than 50% of the algal species were new to this lake and were indicator species of mesosaprobic zone, but indicator species of P-polysaprobic zone are not found. This suggests that the current water quality has declined, but is not deteriorated.