Abstract: Taihu Lake Watershed is one of the areas with acid deposition in China, and acid deposition has a significant effect on the loss of base ions in the basin. The release characteristics of base ions from the representative carbonate rocks and their weathered products as well as the widely distributed sandy loam soil in the watershed under the action of simulated acid solutions with different pH were studied by laboratory simulation tests. The results indicated that: 1)The release of base ions in carbonate rocks was significantly negatively associated with pH and the particle size of acid solution (P<0.01). During the 10 days test period, the minimum release of Ca²⁺ was 0.26 g/kg, and the maximum release was 14.30 g/kg, which was one order of magnitude higher than K⁺, Na⁺ and Mg²⁺. 2)The sensitivity of base ions in the weathered products of carbonate rocks and sandy loam soil to simulated acid solution was in the order of Ca²⁺>Mg²⁺>K⁺. The amount of base ions released was not only related to the pH of simulated acid solution, but also depended on the characteristics of the medium, including its total amount of ions, parent material environment and amount of exchangeable cations. 3)The buffering capacity of different media for simulated acid solution in Taihu Lake Watershed was significant distinction, that was, carbonate rocks>the weathered products of dolomite>the weathered products of limestone>sandy loam soil. It was considered that a large number of carbonates would neutralize protons rapidly, which was the key factor for carbonate rocks and their weathered products to have strong buffering capacity.