Abstract:Stipa purpurea steppe is the largest area and most important community type of alpine steppe ecosystems in Qinghai-Xizang Plateau.Currently,the number of studies on the S.purpurea steppe classification and ordination is still lacking.In this study,the typical S.purpurea steppe in Qinghai Plateau was selected as subject.Multivariate statistics methods including TWINSPAN(Two-way Indicator Species Analysis) and CCA(Canonical Correspondence Analysis) were used to classify the S.purpurea steppe on the basis of investigating a large number of vegetation communities in this region.The results showed that:(1)The species composition of S.purpurea steppe in the study area is relatively simple.The dominant families of seed plants were Gramineae and Compositae,and the dominant areal types of genera were North temperate type.(2)The 90 transects of S.purpurea steppe in Qinghai Plateau could be merged into 8 main ecological associations:Ass.Stipa purpurea+Poa indattenuata,Ass.Stipa purpurea+Kobresia humilis,Ass.Stipa purpurea+Astragalus polycladus,Ass.Stipa purpurea+Kobresia pygmaea,Ass.Stipa purpurea+Potentilla bifurca,Ass.Stipa purpurea+Saussurea arenaria,Ass.Stipa purpurea+Leontopodium humilum and Ass.Stipa purpurea+Kengyilia thoroldia.(3)The major environmental factors influenced the distribution of S.purpurea steppe ecological associations in Qinghai Plateau firstly were space factors(altitude,longitude and latitude) and heat factor(temperature),then water factors(precipitation,wetness).(4)For internal ecological association division of S.purpurea steppe community,CCA could complement and correct the TWINSPAN results,make the classification more realistic ecological significance,and reflect more clearly relationship between the associations and environmental gradients.