35 sampling sites were carried out in the summer of 2014 in Lake Poyang, to explore the spatial distribution characteristics of picophytoplankton during the wet season. The cell abundances of two groups of picophytoplankton were obtained(photosynthetic picoeukaryotes with rich chlorophyll-a and picocyanobacteria with abundant phycocyanin) by flow cytometric analysis directly, which was performed with a FACSJazz flow cytometer unit, while the hetertrophic nanoflagellate should be pre-stained by SYBR Green I dye. In addition, the relationships between the abundance, biomass and net primary production(NPP) of picophytoplankton and the related environmental factors were also considered. Our results showed that, cell abundance of picophytoplankton in Lake Poyang was high, and its average value could reach to 1.04×10⁸ cells/L. Picocyanobacteria dominated picophytoplankton in abundance, especially in the north region of the lake(which connected with Yangtze River), where the proportion of cell abundance between picocyanobacteria and picophytoplankton was more than 80%. The average contribution of picophytoplankton to the NPP and biomass of total phytoplankton could reach to 44% and 46%, respectively. The distribution of picophytoplankton showed spatial variation in Lake Poyang. The abundance and chlorophyll-a concentration of picophytoplankton were the highest in the south region, followed by the north region, and were relatively low in the middle and the east regions. The contribution of picophytoplankton to NPP and biomass of total phytoplankton achieved the highest in the north lake area, reaching to 60% and 50%, respectively. The correlation analysis results showed that the effect of nutrients on picophytoplankton growth was not obvious in Lake Poyang during the wet season. The contribution of picophytoplankton to the NPP of total phytoplankton was negatively related to water transparency. The abundance of picocyanobacteria was significantly affected by water temperature and the density of hetertrophic nanoflagellate, whereas the abundance of picoeukaryotic phytoplankton was related to water pH value.