OTCs were used to investigate the effects of the elevated CO₂ concentration (350, 550 and 700 μmol·mol^-1) and changing precipitation (increased by 30%, increased by 15%, unchanged, reduced by 15%, and reduced by 30%) on antioxidant enzyme, osmotic adjustments and biomass of 2yearold Reaumuria soongorica. The main results of the study is as follows: (1) In June and August,the responses of antioxidant enzyme, SS and Pro, biomass of R. soongorica to changes of CO₂ concentration and changing precipitation were significant, but not include SP in August. (2) With the increase of CO₂, antioxidant enzyme activities, osmotic adjustments, root biomass and above ground biomass of R. soongorica increased, and acclimation occurred during August; MDA content and Root/shoot biomass decreased. (3) With the decrease of precipitation, antioxidant enzyme activities and MDA content increased; above ground biomass decreased; osmotic adjustments, root biomass and root/shoot biomass increased to the precipitation changes. (4) Higher CO₂ and the decrease of in precipitation, R. soongorica have its adaption ways to employ growth adjustment, biomass relocation, increase of root/shoot biomass, promote osmolates accumulation, enhanced the activities of antioxidant enzymes, and decreased lipid peroxidation as well as MDA content. Based on the above results, in the arid and semiarid region, elevated CO₂ concentration can enhance drought resistance ability of R. soongorica to some extent, evaluate the adaption of future climate change.