【Objective】The release of solid aluminum (Al) in soil, induced by exogenous acid, is the primary factor limiting crop growth in acidic soils. Biochar has been demonstrated to reduce the concentration of active Al in soil under equivalent acid input. However, the dynamic mechanisms by which it mitigates Al release remain unclear. 【Method】A stirred-flow dynamic acidification experiment was conducted to comparatively analyze the kinetic processes of solid-phase Al release in soils amended with biochar and Ca(OH)2. 【Results】The results showed that the release of Al from all treatments exhibited a two-stage pattern during acidification: accelerated release followed by decelerated release. These stages can be accurately fitted using piecewise functions combining first-order and pseudo-first-order kinetics (R2 > 0.999). The fitting results suggested that the two stages were controlled by proton diffusion and diffusion of potentially active Al, respectively. At the end of the reaction, the cumulative release of Al from biochar-amended soil was 8.98%-17.23% lower than that from Ca(OH)2-amended soil. In the initial stage, biochar competed for H+ involved in Al release via protonation of surface organic functional groups, and simultaneously reduced the H? diffusion rate constant. This resulted in biochar slowing down the rate of Al release from soil in the initial stage. Peanut straw biochar mainly inhibited Al release at this stage, with a better effect than rice straw biochar. In the later reaction stage, both biochars reduced the soil Al diffusion rate constant by 14.81%–51.06%. Meanwhile, rice straw biochar decreased the content of soil potentially active Al pool by 17.84% and thus reduced the release rate of soil Al during the later stage. Consequently, rice straw biochar was more effective than peanut straw biochar in mitigating soil Al release throughout the acidification process. 【Conclusion】 Biochar can enhance the kinetic stability of soil solid-phase Al release during acidification by improving soil pH buffering capacity, reducing the potentially active Al pool, and optimizing soil pore structure. These findings provide a theoretical basis and technical support for the long-term prevention of Al toxicity in acidic soils.