Abstract: The common 37 annual plants in Alxa desert belong to 9 families and 27 genera, which can be divided into 4 groups, namely annual chenopod, annual short grass, annual artemisia and annual weeds. Annual salsola makes up more than half of the annual plants, followed by short grass and annual artemisia. Annual plants in Alxa desert belong to 12 floristic area-types, and are dominated by temperate Asia, Asia desert, followed by the endemic to Alxa, which indicate the antiquity of Tethys relics and characters of temperate arid desert. The relationship between annual plants biodiversity and environmental factors was analyzed by Twinspan classification, CCA ordination and stepwise regression. The results implied that the key environmental factors affecting annual plant composition and distribution are: the first type is water, heat and sunshine condition, including annual precipitation, accumulated temperature and sunshine hours; the second type is percentage of silt; the third type includes index about saline-alkali levels of soil, containing SO2-4, Mg2+ and HCO-3. Therefore, climate, especially the annual precipitation directly determine the annual plants composition in desert communities, in addition, soil texture also affect their settlement and propagation, which in a certain level examine and verify the theoretic hypothesis about ecological restoration in desert grassland.

Key words: ecological restoration, classification, ordination, stepwise regression