Abstract: By using ion exchange resin membrane as a plant root simulator, this paper studied the variations of soil nutrient availability and enzyme activities in a poplar plantation after applying phenolic acid. The exogenous phenolic acid had significant effects on the soil nutrient availability and enzyme activities, and the effects were concentration and time dependent. With increasing phenolic acid concentration, the extraction mass of soil NH₄⁺-N and NO₃^--N decreased significantly. At high concentration phenolic acid, soil PO₄^3- and Mn²⁺ availability increased significantly while soil K⁺ and Fe³⁺ availability was in adverse, and soil urease and phosphatase activities had a significant decrease while soil catalase and polyphenol oxidase activities increased significantly. With the elongation of incubation time, the availability of soil NH₄⁺-N, PO₄^3-, and Mn²⁺ increased gradually, while that of soil NO₃^--N, K⁺, Fe³⁺, and Zn²⁺ decreased significantly. The correlation analysis showed that the availability of soil NO₃^--N, K⁺, Fe²⁺, and Mn^2+ had close correlations with the activities of soil urease, polyphenol oxidase, and phosphatase.