<p>The aim of this work was to investigate the remediation performance and mechanism of the composites based on alkaline minerals and agricultural wastes to acidified soil. The wollastonite-sodium silicate-biochar composite (Ca-C-Si) and hydroxyapatite-sodium silicate-biochar composite (P–C-Si) were prepared and applied to the remediation of acidified yellow soil with a pH of 4.70 through pot Chinese cabbage experiment. As the dosage of Ca-C-Si and P–C-Si increased from 0.5% to 2.0% of the acidic yellow soil, significant changes in soil characteristics were observed compared to the control. The pH value increased by a maximum of 0.98 and 2.09 units, respectively; the exchangeable acidity, exchangeable hydrogen, and exchangeable aluminum decreased by the maximum of 79.73% and 94.52%, 59.26% and 82.72%, 85.56% and 97.89%, respectively; and the cation exchange capacity and base saturation increased by the maximum of 66.07% and 133.93%, 57.2% and 63.7%, respectively. However, the fresh weight and dry weight of Chinese cabbage reached their maximum at a dosage of 1.5% for Ca-C-Si and 0.5% for P–C-Si, respectively. The dosage of materials needed to be optimal, achieving a balance between soil improvement and crop growth. Infrared spectrum, X-ray diffraction pattern, pH and chemical composition showed that the rape straw was converted to biochar under high temperature and anoxic conditions. The materials exhibited better alkalinity, contain essential nutrients for plant such as calcium, silicon, phosphorus and potassium. The functional groups like hydroxyl and carboxyl on biochar could dissociate to form negatively charged sites, which improved cation exchange capacity and neutralize hydrogen ions. This study demonstrates the improvement effect and mechanism of the two composites on acidic yellow soils, which provides practical guidance for the application of materials in soil remediation.</p>