Abstract: In recent years,after a study of the permian plants in the Xinjiang region,the author has found that the Permian plants in northern Xinjiang（i. e.the Junggar and Turfan basins）in the main belong to the“Angara"flora, that is,are analogous to the Kuznetsk flora in the Kuznetsk basin of the U.S.S.R., but a number of elements of the Cathaysian flora are also mixed in them. The plants in the Tarim basin in southern Xinjiang basically belong to the Cathaysian flora, but some typical elements of the Angara flora are mixed in them at the northern edge of the basin.Therefore,the views that "the Angara flora is younger than the Cathaysian one and overlies the 1atter" （Si Xingjian,1953）and that "the Angara flora is never mixed with the Cathaysian flora" （Si Xingjian, 1953）are incomplete. The bounndary between the two major floras of northern and southern Xinjiang is roughly drawn at about 1at. 42°N,i.e.roughly coincides with the first latitudinal structural belt（the Tianshan-Yinshan structural belt）so called by Prof.Lee Ssu-kuang,and the phenomenon of mixing of the elements of the two major flora may still appear within the boundary zone and to the north and south of it. Then this paper deals with the Permian flora in the Tibetan region, i.e. the Gondwana flora in southern Tibe（tsouth of the Yarlung Zangbo River）and the Cathaysian flora in northern Tibet（notrh of the Yarlung Zangbo River）.The boundary between the two major flora provinces roughly lies along the Yarlung Zangbo River valley （i.e. the Yarlung Zangbo fracture） ,that is to say, the boundary happens to coincide with the suture between the Indian plate and the Eurasian plate.This supports some view-points of the theory of plate bectonics and indicates that the important significance of the results of the flora research in the plateteconics theory cannot be neglected. The paper also emphasizes that during the Permian there were two worldwide first-order floras-the Angara and Cathaysian floras-in western China（Xingjiang and Tibet）. On the other hand, the Gondwana flora in southern Tibet did not grow in place but was brought there owing to the northward migration of the Indian plate of the Gondwanaland in the southern hemisphere and its collision against the Eurasian plate.In this paper it is for the first time called the "secondary spreading" flora. Such spreading is not a phenomenon of slow migration of organisms as generally considered, but a kind of spreading of "transport" character in the manner that autochthone acts as a carrier The theory of plate tectonics and the plate movemen will bring new concepts and theories to large-scale migration of biocoenosis.