To study the effect of CO_2 concentration on carbon assimilation and water use efficiency of apricots, and to learn more about growth potential and ecological advantages of apricots under elevated atmospheric CO_2 and global warming, the author measured photosynthesis parameters of 15 2-year-old apricot varieties with a Li - 6400 portable gas analyzer under natural CO_2 concentration, half CO_2 concentration, doubled CO_2 concentration and tripled CO_2 concentration. The results showed that there was a significant change on photosynthesis of apricots under the instantaneous variable CO_2 concentration conditions. While CO_2 concentration was elevated, the maximum photosynthesis rate, apparent quantum yield and water use efficiency increased, dark respiration rate and light compensation point decreased, light saturation point increased nonsignificantly, and the response of stomatal conductance and transpiration rate had some differences. Under the appropriately elevated CO_2 concentration conditions, lower light and water were made better use, photosynthesis was promoted, assimilates of leaves were increased and carbon cycle was accelerated.