Abstract: The analysis on observational data from herbage of grassland in region around the Qinghai Lake in Qinghai Province indicated that the variation coefficient of Poa crymophila in plant community was small,being 50%～100%,the least one was Aneurolepidium, but the Stipa purpurea was the largest one being 75%～ 200%,which was one of the dominance plant with largest variation coefficient. The species of Stipa purpurea, Artemisia scoparia and Poa crymophila,which was not stable for yearly changes of plant composition, displayed their character of weak resistance to dry and of the sensitive to dry, the Carex condilapis and Aneurolepidiu had strong adaptability of climate and showed strong resistance to dry, that yearly change of plant composition was stable. The Carex condilapis had strong adaptability of climate and resistance to dry, but the water condition is still main climatic factor which controlled its growth, the monthly change of its density always decreased by month.