Abstract: By using free air CO₂ enrichment (FACE) system, a pot experiment under field condition was conducted to study the effects of elevated CO₂ concentration (550±60 μmol·mol^-1) on the leaf photosynthesis and chlorophyll fluorescence parameters of mung bean. Comparing with the control (CO₂ concentration averagely 389±40 μmol·mol^-1),elevated CO₂ concentration increased the leaf intercellular CO₂ concentration (C_i) and net photosynthesis rate (P_n) at flowering and pod growth stage by 9.8% and 11.7%, decreased the stomatic conductance (G_s) and transpiration rate (T_r) by 32.0% and 24.6%, respectively, and increased the water use efficiency (WUE) by 83.5%.Elevated CO₂ concentration had lesser effects on the minimal fluorescence (F_o), maximal fluorescence (F_m), variable fluorescence (F_v), ratio of variable fluorescence to minimal fluorescence (F_v/F_o), and ratio of variable fluorescence to maximal fluorescence (F_v/F_m) at bud stage, but increased the F_o at pod filling stage by 19.1% and decreased the F_m, F_v, F_v/F_o, and F_v/F_m by 9.0%, 14.3%, 25.8%, and 6.2%, respectively. These results suggested that elevated CO₂ concentration could damage the structure of leaf photosystemⅡ and consequently decrease the leaf photosynthetic capacity in the late growth phase of mung bean.