Abstract: 【Objective】The study was to evaluate the effects of doubling the CO2 concentration on photosynthetic characteristics and growth of Dendrobium offi cinale.【Method】With the autumn buds of D. offi cinale as test materials, the effects of treatments with CO2 concentration of 400 μmol/mol (atmospheric concentration, control) and 800 μmol/mol (treatment concentration) for 180 days on the photosynthetic characteristics, growth and effective components of D. officinale were compared. 【Result】After doubling the CO2 concentration, the net photosynthetic rate, stomatal conductance, transpiration rate and water use efficiency of D. offi cinale were increased significantly compared with those of the control, however, there was no photosynthetic acclimation on D. offi cinale during the experiments. The stem dry weight, stem fresh weight, stem height, numbers of leaves and leaf thickness were also significantly increased in double treatment, with the increases of 30%, 13%, 49.3%, 42% and 3.5%, respectively, while the single leaf area and the specific leaf area were decreased by 11.8% and20%, respectively. The soluble protein content in leaf was increased by 19%. The contents of polysaccharides, alkaloids, total amino acids and total flavonoids in stem were slightly improved, but there was no significant difference compared with those of the control.【Conclusion】The growth of D. offi cinalis could be promoted by doubling the CO2 concentration, and the yield of its main medicinal part (stem) was increased.