Abstract: The adsorption behavior of heavy metals in soil is affected by the acid-base properties of soil surface. The acid yellow soil in Guizhou Province is severely polluted by cadmium. Studying the adsorption characteristics and morphological changes of cadmium in yellow soil is thus of great importance for preventing and remediating cadmium contamination. Sandy shale yellow soil samples at different depths in Baihuahu Town, Guizhou Province were selected in this research. Based on the results of continuous acid-base potentiometric titration experiments, the 1-site/2-pK_a surface complexation model (SCM) was used to explore the surface acid-base properties of these soils. The SCM was used to simulate the adsorption behavior and speciation distribution of Cd in the yellow soil under different pH conditions. Besides, the correlation between the yellow soil composition and surface acid-base properties was analyzed. Firstly, SCM calculations indicated that the soil surface sites (H_s) concentrations in humus layer (0-45 cm), leaching layer (>45-57 cm), deposition layer (>57-81 cm), regolith (>81-110 cm) and parent material layer (>110-183 cm) had a general decreasing trend with depth, which were 0.120, 0.090, 0.097, 0.056 and 0.055 mol/L, respectively. While the point of zero charge (pH_pzc,SCM) showed an opposite trend, which were 4.83, 4.71, 4.61, 4.96 and 4.98, respectively. The pH_pzc,SCM data were close to the experimental data (pH_pzc,M), and their change trends were consistent, indicating that it was feasible to apply 1-site/2-pK_a SCM to study the acid-base properties of the yellow soil. Secondly, Cd was gradually adsorbed with the increasing of pH and reached complete adsorption at pH=7. The concentrations of dissolved and adsorbed of Cd at different pH calculated by SCM were in good agreement with the experimental adsorption data (correlation coefficient R≥0.995). In addition, the experimental adsorption behavior of Cd was consistent with the simulation results of the three species (≡SOH₂⁺, ≡SOH, ≡SO⁻) distribution in yellow soil surface sites at different pH. The ≡SOH₂⁺ and ≡SO⁻ were the main surface species of the soils at pH<pH_pzc and pH>pH_pzc, respectively. This revealed the influence mechanism of the acid-base properties of the yellow soil surface on the adsorption behavior of Cd, which further showed that SCM was suitable for describing the adsorption characteristics of Cd with soil pH. Thirdly, correlation analysis showed that organic matter and free iron oxide played important roles in H_s, and the pH_pzc of soil at different depths was mainly controlled by inorganic colloids such as clay minerals and quartz. These results showed that 1-site/2-pK_a SCM could accurately describe the surface acid-base properties, Cd adsorption characteristics and morphology distribution of acidic yellow soil in Guizhou Province, which provide a new idea for studying the migration and transformation behavior of heavy metals in soil.