To investigate the effects of increased tannic acid input on the migration of major soluble metals in soil after converting native forests to eucalyptus plantations, a 21-day indoor incubation experiment was conducted. The study analyzed the leaching of soluble Fe, Al, Mn and Zn under different moistures (50%, 70% and 90% water-holding capacity, denoted as W5, W7 and W9) and decomposition solutions with equal carbon content but varying tannic acid levels (eucalyptus leaves, EU; rice straw, RS; blank control, CK). The results showed that: 1) Soil moisture significantly influenced metal release. W9 promoted the leaching of soluble Al and Mn leaching, W7 inhibited soluble Fe, while W5 reduced soluble Mn and Zn. 2) The high-tannic EU solution significantly inhibited the leaching of soluble Fe, Al, Mn and Zn, with the leaching order being EU < RS≤CK. RS and CK significantly increased soil pH compared to EU, indicating that EU helped maintain soil pH stability. 3) The leaching dynamics of soluble Fe, Al, Mn and Zn exhibited temporal heterogeneity, peak leaching occurred at 15, 15, 3 and 0 d, respectively, while the lowest leaching occurred at 21, 21, 10 and 15 d. The leaching peaks of Mn and Zn appeared earlier than Fe and Al. In conclusion, tannic acid input from eucalyptus inhibits the migration of soluble Fe, Al, Mn, and Zn by maintaining acidic soil pH and metal complexation, with moisture modulating the strength of this inhibitory effect.