Abstract: We used an OTC (open top chamber) system to study the effects of elevated CO₂ concentration (atmospheric CO₂ concentration + 200 μmol·mol^-1) on the growth and photosynthetic physiology of Hylotelephium erythrostictum. Elevated CO₂ concentration decreased the leaf stomatal density of the upper and lower epidermis of H. erythrostictum by 16.1% and 16.7%, respectively. Elevated CO₂ concentration increased the vascular bundle in leaves and the cell volume near the upper epidermis. Elevated CO₂ concentration significantly increased the photosynthetic pigments content, net photosynthetic rate, stomatal conductance and transpiration rate of H. erythrostictum at night. In the evening of initial flowering stage, elevated CO₂ concentration significantly reduced the malic acid content by 64.0%, while increased cellulose content by 20.8%. In the morning of full flowering stage, elevated CO₂ concentration significantly increased the malic acid content by 27.0%, but had no effect on carbohydrate content. Elevated CO₂ concentration increased the number of branches per plant, stem mass and total biomass of H. erythrostictum. Elevated CO₂ concentration was beneficial to the growth of H. erythrostictum.