Abstract: The area of the Karakorum-Kunlun Mountains is not so rich in flora. 827 species, subspecies and varieties of higher plants were recorded in the area of ca. 400, 000km2. Those plants belong to 272 genera of 60 families. Among them there are only 5 fern species of 3 genera of 3 families and 14 gymnosperms of 3 genera of 3 families. There are 136 grass species (Gramineae). The families each of which have more than 50 species observed there were Compositae, Leguminosae, Cruciferae, Cyperaceae and Chenopodiaceae. Of the taxa in the area, 44.5% belongs to the Central Asian geographic elements and 21.7% to Qingzang Plateau elements in terms of genera. But the Qingzang Plateau elements dominated in the sections of the Kumkol Basin of the Middle Kunlun (see Fig. 1 Ⅰ 5), the southern flank of east part of the West Kunlun (Ⅱ 2) and the southern flank of the Middle Kunlun (Ⅱ 3). The higher the altitude of the belts is, the greater the proportion of Qingzang Plateau geographic elements is . The proportion of Centra Asian elements decreases while the proportion of the Qingzang Plateau elements increases as the altitude raises. These two elements are similar in proportion at ca. 4250 m above sea level. The floristic differentiation between the southern and the northern flanks of the Kunlun is much more apparent than that between the West and Middle Kunlun. The results of this study show that the demarcation line between the Central Asian sub-region and the Qingzang Plateau sub-region runs along the Karakorum-Kunlun Mountains.