Abstract: The present paper gives a preliminary study of the pigment sources in the lake sediments and community structures of the phytoplanktons in some lakes on the Qinghai-Xizang Plateau. The results of research show that total organic carbon (TOC) contents in the lakes mostly vary between 4% and 6%, and the aquatic pigments come mainly from algae and bacteria in the lakes. Oscillatoriaceae and Arthrospira platensis (cyanobacteria) have a marked advantage of growth in the phytoplanktons in the lakes on the Plateau. The number of Oscillatoriaceae is much more than that of Arthrospira platensis. The dissolved oxygen (DO) and specific conductance (SC) have an important effect on the phytoplanktons in the lakes. In particular, the increase of the specific conductance may restrain the growth of the phytoplanktons in the lakes.