Cushion plants are important elements in alpine subnivalbelt flora, which are recognized as the production of adaptive convergence to cold and extreme environment in alpine zone. In this study, the seeds of five cushion plants of Caryophyllaceae were chosen asexperimental materials. These seeds that collected from the alpine subnival belt in Xizang and Yunnan, germinated on wet filter papers. Roottipsquashmethod was used for cytological observation. The present study aims to accumulate karyological data for cushion plants in QinghaiTibet Plateau (QTP), and then further to provide the basis for the exploration on karyotypic evolution mechanism of special life form plants in extreme environment of QTP. The results showed that five species are all diploid, and their karyotype formulae were showed as followed: Arenaria densissima, 2n = 2x = 20m + 2sm, 2A; A. oreophila, 2n = 2x = 22m, 1A; A. polytrichoides, 2n = 2x = 20m + 2sm, 2A; A. smithiana, 2n = 2x = 20m + 2sm, 1A; Thylacospermum caespitosum, 2n = 2x = 18m + 4sm, 2A. The chromosome numbers of T. caespitosum is consistent with that of Arenaria subg. Dolophragma. The results provide the karyological evidence for the independence of the new clade composed by abovementioned two taxa in the molecular phylogeny framework of Caryophyllaceae. Moreover, we discussed the association between the evolutionary history of paleopolyploid speciation exhibited by five studied cushion plants and the uplift of QTP and its surrounding region during the Miocene period.