Abstract: In this study, the pH gradient of acid soil in subtropical hilly region was selected, and the organic mineral complex mechanism of soil organic carbon stability under different pH conditions was revealed by combining the soil organic carbon composition, related enzyme activities and microbial community composition. The results showed that: 1) when pH was lower than 5.0, the long-term sequestration of soil organic carbon in forest land was mainly in the form of mineral bound organic carbon (maoc), while the cultivated land was more in the form of particulate organic carbon (POC), and the carbon stability was significantly lower than that of forest land; 2) Microbial community composition is the key driving factor for the difference of soil organic carbon composition under the two types of land use. Fungi are dominant in forest land (fungi/bacteria ratio > 2.1), while bacteria are dominant in cultivated land; 3) The effect of pH on soil enzyme activity showed significant differences in different land use patterns: when pH < 5.0, the activity of hydrolase was inhibited, and the activity of oxidase increased to accelerate the decomposition of stubborn carbon; In woodland, hydrolase was active when pH > 5.0, and oxidase was activated when pH < 5.0. The study suggested that in the acid soil area, the cultivated land should be reduced and fertilized to strengthen maoc protection, while the forest land should maintain fungal diversity to optimize the coupling process of carbon, nitrogen and phosphorus, providing a new idea for the adaptive management of ecosystem under the background of soil acidification in the subtropical hilly region.