The study of deep sea (>200 m) plankton is the frontier of marine biology and ecology research in China. Summarizing existing knowledge of deep sea plankton is important to Chinese research in this field. Most phytoplankton will die when they settle out of the euphotic zone. However, some phytoplankton manages to survive in the deep sea despite of the darkness. This review synthesized the research of living phytoplankton in deep sea. Phytoplankton needs sunlight to carry out photosynthesis. There were only 18 species of phytoplankton found in the deep sea with the maximum depth of 4000 m. The abundance of coccolithphore was higher than that of diatoms and dinoflagellates. Maximum abundance of coccolithphore in the deep sea was 2220 cells/L in the depth of 500 m. In the years 1911-1985, the olive green cells were found in deep seas. There was no extensive taxonomic definition of olive green cells due to limited research devices. After the year 1985, the olive green cells was deemed as Synechococcus spp., which was found in 2750 m. Maximum abundance of Synechococcus spp. found in deep sea was 3.5 ×10⁵ cells/mL at a depth of 800 m. In situ fluorescence profiles in the deep sea found tertiary phytoplankton pigment maxima in 20-700 m depth. However, we are not sure what organisms caused the fluorescent maxima. There was little information about the biomass of phytoplankton in the deep sea. In the limited studies, phytoplankton biomass (0.001-0.1μg C/L) decreased with depth from 300 m to the bottom.