OTCs were used to investigate the effects of the elevated CO_2 concentration (350,550 and 700 mumol·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.soongoricato changes of CO_2 concentration and changing precipitation were significant,but not include SP in August. (2) With the increase of CO_2,antioxidant enzyme activities,osmotic adjustments,root biomass and above ground biomass of R.soongoricaincreased, 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 CO_2 and the decrease of in precipitation,R.soongoricahave 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 CO_2 concentration can enhance drought resistance ability of R.soongoricato some extent,evaluate the adaption of future climate change.