Abstract: All the C4 plants in the arid area of Xinjiang were identified according to the stable carbon isotope ratios contents and some related 1iteratures． There are 278 species of C4 plants from 66 genuses in 12 families. The taxonomy,life form,geographical element and the areal-types of genera were accordingly analysis. The results showed that the families with most species orderly from Chenopodiaceae，Gramineae，Cyperaceae，Liliaceae，Polygonaceae etc. Among which,the dicotyledon more than monocotyledon of angiosperm ，there is not C4 plants in the pteridophyte and the gymnosperm. Annual and perennial of C4 plant dominate in the arid area of Xinjiang. This reveals these species compete with a betteradapted and more powerful succession evolution. The dominant of C4 plants species occupy accounts for 10%. Among C4 plants 125 species grow in sand dune，103 species grow in salt and alkaloid environment，56 species grow in wet environment. Everything prove C4 plant might have higher tolerance to environmental stresses (dry and salting)and could make greater contribution to sand land restoration of botanic characters． Furthermore,The floristic composition of C4 plants is concisely enumerated and were found to belong to 10 categories,which the dominant element of the geographical composition was Mediterranea，W．Asia to C．Asia and there are 13 genera and 60 species in this region. The distribution of the florae reflects the dynamic climatic and geological changes during the species succession on a historical scale. Therefore，it is suggested to carry out the study on breeding，introduction and popularization of C4 plants and so as to solve desertification in the arid regions in northwest China．The complete investigation of the plant resources and their distribution and succession in the region will provide the scientific basis for protecting the plant resources in the region.

Key words: the arid area of Xinjiang , C4 plants, geographical distribution, floral elements