【Objective】At mospheric CO_2 concentrations would increase from approximately 350 mumol·mol~(-1) today to over 700 mumo·mol~(-1)by the end of this century. The elevated CO_2 islikely to have profound effects on the precipitation pattern in the future. This change would seriously affect the desert ecosystem,photosynthesis,above-and belowground biomass of desert plants,which could lead to the changes of ecosystem structure and function. Although many studies have examined the effects of precipitation and CO_2,the interaction of changing precipitation pattern and elevated CO_2 concentration on desert plantsis still not clear.【Methods】A pot experiment was conducted to study the interaction of elevated CO_2 concentration and changing precipitation pattern on photosynthesis parameters such as photosynthesis rate and transpiration rate and so on,andon growth characteristics such as plant height,biomass and root /shoot ratio (R/S) of Reaumuria soongarica thatis a dominant plant species of desert steppe in the arid region of China,in order to assess the possible effect of global climate change on desert ecosystem. The two-year-old seedlings were subjected to two CO_2 concentrations (350 and 700 !mol ·mol~(-1)) and three precipitation levels [natural precipitationas control (0), precipitation minus 30% (-30%),precipitation plus 30% (+ 30%) ].【Result】Doubled CO_2 concentration increased the photosynthesis rate and decreased the transpiration rate and stomatal conductance (P < 0. 05). The increase of precipitation by 30% had a significant promoting influence on the photosynthesis rateunder the elevated CO_2, and a certain compensation effect on the transpiration rate and stomatal conductance inhibited by the elevated CO_2. Long-term treatment with increased CO_2 led to the photosynthetic acclimation by reducing the photosynthetic capacity. Elevated CO_2 concentration and increasing precipitation were able to significantly stimulate the increase of plant height,aboveground biomass and total biomass of R. soongarica,and the elevated CO_2 concentration reduced the decrease of the R. soongarica growth caused by the decrease of rainfall. Root biomass were increased under precipitation reduction by elvated CO_2 concentration.