Abstract: Maqu county is located in the southwest of Gansu Province, on the northeast of the Qinghai-Xizang Plateau. Maqu meadow is the core region of the important water source supply area of the Huanghe River, having unique significance in the water and eco-environmental security of the Huanghe River basin. A lot of remarkable results in the variation of Maqu meadow are achieved from the perspective of climate and eco-environment, but phenological variation of the pasture grass in Maqu meadow isnts paid enough attention. Based on the growing data of Elymus nutans (1985—2005) at the agricultural meteorological station of Maqu (102°05′E, 34°00′N, sea-level elevation 3471.4 m) and the simultaneous observation meteorological factors (such as temperature, precipitation, sunshine duration, etc) at the same place, the relationship between the Elymus nutans phenological variation and the meteorological factors is studied, providing reference for the research on eco-environment variation of Maqu meadow.In recent 20 years, the Elymus nutans recovery date of Maqu meadow shows a delaying trend with the tendency ratio of 1.6 d/10 a, but the date of ear, bloom, maturate and withered show obvious advancing trends with the tendency ratios of 4.9 d/10 a, 8.0 d/10 a, 13.9 d/10 a and 1.3 d/10 a. The reducing of autumnal precipitation is main impact factor to delaying tendency of recovery date. The rising of summer temperature results in the advancing trend of Elymus nutans ear, bloom and maturate date in Maqu meadow, and the warming and drying trend of autumn is the main impact factor of the advancing Elymus nutans. The impact of these phenological changes on the Elymus nutans quality, yield and the quality of seeds need further research.Compared with Elymus nutans, the observation duration of other grass is less in Maqu meadow, so their phenological variation is not analyzed, which requires further research. Besides, the impact of the grass phenological variation on animal husbandry and eco-environment in Maqu meadow need further study too.