Abstract: The effects of elevated atmospheric CO₂ concentration and Pb contamination on organic compounds and microbial characteristics in rhizosphere soil of Robinia Pseudoacacia L. seedlings are investigated via open-top chambers combing with pot experiment. The results show that: 1) Elevated atmospheric CO₂ increased the concentration of TOC, DOC, MBC, total souble sugars, phenolic acids, amino acids, and organic acids inrhizosphere soils, leading to an increase in the activity of bacteria, fungi, actinomycetes and FDA. Except for L-asparaginase, the activities of urease, dehydrogenase, invertase, and β-glucosidase are enhanced, while the pH of soil has little change under elevated CO₂ concentration. 2) With Pb contamination, the concentrations of TOC, total souble sugars, amino acids, organic acids, and L-asparaginase increase, but the DOC, MBC, phenolic acid concentration, urease, dehydrogenase, invertase, and β-glucosidase activity are in decline. The number of bacteria and fungi declines slightly (4.06% and 4.53%, respectively), by contrast, that of actinomycetes and FDA drops largely (12.86% and 10.89%, respectively) under Pb stress. Comparing with Pb contamination, ECO₂ + Pb contamination enhances soil organic compounds and microbial characteristics. Redundancy analyses (RDA) show that the total souble sugars, phenolic acids, MBC, and pH are the principle influence factors for rhizosphere microenvironment. The soil organic compounds are closely related to soil microbial characteristics. The results show that the increased organic compounds under elevated atmospheric CO₂, which is the major factor for relieving the impact of Pb contamination on the rhizosphere microenvironment of Robinia Pseudoacacia L. seedlings.