Abstract: Dynamics of the aboveground, underground and total biomass of the alpine meadow grassland in the north shore of Qinghai Lake were studied from May to September, 2007. The result showed that the curve of seasonal dynamic of the aboveground biomass was single apex, the minimum biomass was at the initial growing period and the maximum in middle August, 223.0 g/m2.The distribution pattern of the underground biomass was Inverted Pyramid type. The underground biomass at the depth of 0-10, 10-20, 20-40 cm showed N type from May to September, biomass at the depth of 0-10 cm accounted for to 65% of the total. The turnover value of the underground biomass was 0.45. The underground biomass accumulation were much larger than that of the aboveground in growing season, and the peak value of the underground biomass was earlier than that of the aboveground, the root/shoot ratio of the community showed a decrease first and followed by a increase, the average was 16.1.