Abstract: Addressing the critical challenge of widespread low- and medium-yielding croplands in China (accounting for 68.76 percent of total arable land) and soil degradation threatening food security, this study systematically investigates the potential and mechanisms of biochar in improving cultivated land quality. This is achieved by integrating literature data on biochar production techniques, physicochemical properties, and its interactions within the soil-microbe system, supplemented by experimental validation. The systematic analysis encompasses: 1) physicochemical characteristics (microporous structure, surface functional groups) of biochar derived from diverse feedstocks (e.g., rice husk, straw, pomelo peel) at pyrolysis temperatures ranging from 300°C to 500°C; 2) major types of low- and medium-yielding soils in China and ameliorative measures targeting specific constraints; 3) multidimensional regulatory effects of biochar on these soils, including soil nutrients, structure, microbial communities, and soil gases; 4) Potential risks associated with biochar application. Key findings reveal that: 1) biochar’s pore structure (specific surface area up to 1059.85 m²/g) and surface functional groups (e.g., hydroxyl, carbonyl) significantly enhance soil structure (reducing bulk density by 11.6% to 18.2%) and water retention capacity (increasing field capacity by 15% to 30%) through physical adsorption and chemical complexation, with effects being more pronounced for biochar derived from higher carbon-content feedstocks. 2) by adjusting soil C/N ratios (increasing to 56.41-94.3) and pH (ameliorating acidic soils towards neutrality), biochar activates beneficial microorganisms (e.g., increasing the relative abundance of Sphingomonas by 20% to 40%) while suppressing pathogens (e.g., decreasing Fusarium abundance by 14% to 32%),thereby restructuring the soil microbiome. This effect is particularly significant in continuously cropped fields. 3) biochar contributes to carbon sequestration, reducing agricultural greenhouse gas emissions (CH₄ by 16.8% to 32.9%; N₂O by 22% to 47%) while synergistically increasing soil organic carbon stocks (by up to 64.3%). Long-term application (over 3 years) yields more stable benefits. This research demonstrates that biochar operates through a tripartite mechanism—“soil structure improvement - microbial community optimization - carbon and nitrogen cycle regulation”—effectively enhancing the productivity of low- and medium-yielding croplands while delivering ecological benefits. It thus offers an innovative solution supporting China’s goals for cultivated land protection and carbon neutrality. Future research should prioritize investigating long-term ecological risks (e.g., heavy metal accumulation, volatilization of toxic substances) and establishing standardized application protocols.