Based on field investigations and laboratory works,variations of species diversity and biomass of meadow steppe and relations between them with climate factors were studied during growing season in Qilian Mountains. The results indicated that the plant community type of Elymus nutans,Polygonum viviparum,Stipa purpurea is changing into that of Carex atrofusca,Gueldenstaedtia verna,Potentilla mulatifida,which exhibited meadow steppe tend to step at lower elevation and approach to meadow at higher elevation,whiles species richness and diversity show a decreasing trend from 2 950 m to 3 250 m. Species diversity in 2 950 m is the most abundant in July,whereas it is later one month in 3 250 m,which due to the delay period from germination to steady growth under lower temperature in higher elevation. For plant communities in 2 950 m and 3 250 m, species evenness and dissimilarity are the greatest in July,and this occur for species similarity in August, they are overgrow periods of plant growth. The change of species diversity is related to different growth periods for different plant community types. During growing season,the above-ground biomass value is the maximum in August at 2 950 m,whereas it appears in September at 3 250 m,and the month accumulation maximum of above-ground biomass appears in June at 2 950 m,but it is later one month at 3 250 m. Above-ground biomass of meadow steppe is sensitive to climate changes before one and two month earlier than growing season and the sensitivity to temperature is more obvious than to precipitation in Qilian Mountains.