Abstract: Two cruises were carried out in Nandagang wetland in 5th January and 13th March of 2016. Phytoplankton samples were analyzed and 108 taxa belonging to 74 genus of 7 classes were identified. In January, the cell abundance of phytoplankton ranged (0.26~6.70)×10⁷ /L, the average abundance was 2.25×10⁷ /L. The dominant species were Chlamydomonas sp.、Cyclotella sp.、Merismopedia minima、Kirchneriella sp. and Carteria sp. In March, the cell abundance of phytoplankton ranged (0.35~16.35)×10⁷/L, the average abundance was 4.28×10⁷/L. The dominant species were Chlorella sp.、Merismopedia minima)、Carteria sp. and Ankistrodesmus acicularis. The Shannon-Wiener index (H') is generally lower than that of the tourist center and the cruise terminal near the center of the cruise ship, which may be related to the suspension of the icing period. From the biodiversity index, the water quality of wetland is quite clean during freezing period, the phytoplankton resources are abundant and structure is relatively stable, and the biodiversity after melting is better than that in the freezing period. Due to the heterogeneity of environmental factors of space, distribution and density of species change quite a lot among various stations at the same period.