Abstract: The floristic features of the sand vegetation in the middle reaches of the Yarlung Zhangbo River are discussed．From the geographic elements of the floristic it can be seen that the endemic species are quite rich．Among 82 main edificatos and common companions，31 species are endemics，and most of them are neoendemics，which have differentiated from their ancestors in the adjacent floras，but there is almost no endemic genus．It indicates that the sand flora is a new and young one．The floristic elements also show that the flora is neither totally derived nor entirely native，and it has formed based on the East-Asian element． Meanwhile，the migration and percolation of the adjacent floristic elements have taken place during the lift of the Qinghai-Xizang Plateau．

Key words: Sand vegetation, Geographic element, Florogenesis