Abstract: The flora of northwest china belongs to the Holarctic Kingdom in Chinese flora, the flora of the south of northwest China belongs to a Subregion in the Central China Region in the Japan-China Forest Subkingdom, and the central-east belongs to a Subregion in the North China Region in the Japan-China Forest Subkingdom, and the southwest belongs to a Subregion the Tibetan Pleteau and the Himalaya-China Forest Subkingdom, and the North belongs to a Subregion the Asia Desolate and Boundless Forest Subkingdom. There are 1 729 species (including infraspecific taxon) of woody plants belonging to 103 families and 338 genera (exclude cultivated plants) in northwest China. Among them, there are 57 species belonging to 17 genera and 6 families are of gymnosperm and 1 672 species belonging to 321 genera and 97 families are of angiosperm. In addition, there are 26 Chinese endemic genera and 173 northwest China endemic species. In those plants, the big families and the big genera play important roles. The flora of northwest China can be divided into 15 distribution types and 17 subtypes. Among them, North temperate, Pantropic, E. Asia &N. Amer. Disjuncted, E. Asia are important types. Based on the analysis of compositions and the geographical elements and characteristics of the flora, the paper has discussed the major characteristics of the flora as follows: Species are comparatively rich;species and floristic elements are striking difference;the geographical elements of the flora are comparatively complex, and the genera of temperate are the dominant areal types, among them, north temperate play the part of an important role in the flora;the flora is ancient origin;endemic woody plants are comparatively rich;the flora has widely relate to other area, and the flora is the crisscrossing and assembling, mixing and transition of diversified floristic elements.

Key words: woody plants, flora, characteristics of the flora, northwest China