Abstract: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 2yearold 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 semiarid region, elevated CO2 concentration can enhance drought resistance ability of R. soongorica to some extent, evaluate the adaption of future climate change.