Abstract: An attempt has been made in this paper to describe briefly the characteristics, ecological environments and the origin of the subnival vegetation of Xizang based on the information collected in the field. 1. This snbnival vegetation of Xizang is distributed in the subnival zone between the continual plant cover line and the permanent snow line on the alpine zone. The climate is severe. The vegetation is primitive, being composed mainly of some lower plant com- munities, mosses communities and some mesophytic flowering plant communities in spots. It is lower and sparse and can be classified into three major types, as follows: (1) Type of humid climate in the southern slopes of the eastern ttimalaya and Kangrigarbo rang. (2) Type of subhumid climate in the eastern Xizang. (3) Type of arid and semiarid climate in the central and western Xizang. 2. The mieroclimate plays a decisive role in the existence and development of the subniwfi vegetation. To the severe conditions, plants also wisely adapt, utilizing whatever water and heat available, completing their growth and development stages in a very short period, and resisting to cold and other unfavorable factors. 3. Frmn the analysis of the cmnposition of the flora of subnival vegetation in Xizang, it is shown that the subnival vegetation has evolved from alpine vegetation of Xizang and the neighbour region to eastern Xizang and southern Xizang.