Pot experiments were conducted to study the co-effects of elevated CO_2 concentration and changing precipitation on growth characters of Reaumuria soongorica,a dominant of desert steppe in the arid region of China,in order to assess the possible effect of global climate change on desert ecosystem. The main plot contained three CO_2 concentrations (350,5 00 and 700 mumol·mol~(-1)) and five precipitation levels[natural precipitation as control (0), precipitation minus 30% (- 30%),precipitation minus 15% (- 15%),precipitation plus 15% (+ 15%),precipitation plus 30% (+ 30%) ]. The results showed that in June,July and August,elevated CO_2 promoted the increase of plant height,aboveground biomass,root biomass and total biomass of R. soongorica under five precipitation conditions,and CO_2 fattening effect on the growth in increased precipitation was bigger than that of in decreased precipitation. In June and July,root mass fraction and root / shoot ratio were decreased with elevated CO_2 concentration under five precipitation conditions,and only in August,root mass fraction and root / shoot ratio of R. soongorica were enhanced by elevated CO_2 under - 15% precipitation. In conclusion,elevated CO_2 concentration would promote R. soongorica to accumulate more aboveground biomass to abtain more resources when precipitation is increased in the future; elevated CO_2 concentration would stimulate this plant distribute more belowground biomass to adapt drought environment when precipitation is decreased in the future,but the effect was limited by the amount of precipitation and processing time.