Soil acidification poses a significant threat to the healthy development of agriculture. Traditional soil amendment involving lime (L) has notable limitations. Therefore, developing alternative soil acidification amendment methods to address soil acidification holds significance. In this study, calcium lignosulfonate (LC) was introduced to different acidic purple soils to assess its efficacy in reducing soil acidity and enhancing soil fertility. The density functional theory (DFT) calculation was employed to analyze the potential interaction mechanisms of LC in decreasing soil acidity. The results indicated that the 2 parts per thousand LC addition improved the pH by 2.8 and the soil organic carbon by 26 % in poor-quality and extremely acidic purple soil (with an initial pH of 4.4) after a 40 -day soil pot experiment. The findings from the Fourier Transform infrared spectroscopy (FTIR) and DFT calculation suggested that the competitive adsorption between Al 3 + and Ca 2 + on the surface functional groups ( e.g. , - SO 3 - and - OH) of LC contributes to the immobilization of soil exchangeable Al 3 + . These results validate the feasibility of LC as an alternative to lime application for amending extremely acidic soils and underscore its advantages for soil fertility enhancement. The results of the molecular model calculation extend the understanding of the key mechanisms of LC mitigating soil acidification. This study will highlight the potential of LC in agricultural applications and contribute to the development of more effective soil amendments to ensure cropland health and promote sustainable agriculture.