<p>Understanding the coupled processes of soil biochar carbon sequestration and contaminated soil treatment is of great significance for achieving carbon neutrality and addressing global climate change. The coupled technology of soil biochar carbon sequestration and contaminated soil treatment has broad application prospects. Based on the key characteristics of biochar, this paper focuses on analyzing the carbon sequestration effect and contaminated soil treatment effect of soil biochar from the perspective of mechanism analysis. It also explores the coupling and synergistic relationship between biochar application in domestic source organic contaminated soil treatment and carbon sequestration, as well as the key scientific issues. Research shows: There is a coupling relationship and synergistic effect between carbon sequestration in biochar-amended soil and organic contaminated soil treatment. The key basic scientific issue of the coupling effect between biochar carbon sequestration and soil treatment in domestic source organic contaminated soil is to inhibit the degradation, transformation, migration, and release of organic pollutants. The multi-stage and multi-mechanism inhibition of organic matter degradation by soil biochar, as well as the mechanisms and methods of directional transformation and migration regulation, will be the main research directions in the next step. The carbon sequestration effect of soil biochar is significant. After adding biochar to soil, there are mainly three carbon sequestration mechanisms: direct burial, inhibition of organic matter degradation, and regulation of directional transformation and absorption. Both the environmental and engineering treatment effects of soil biochar on contaminated soil are remarkable. The environmental treatment mechanism of biochar is the adsorption and fixation of organic pollutants in soil. The engineering treatment mechanism is that adding biochar to organic contaminated soil can change soil mechanical properties (such as cohesion, internal friction angle, and soil shear strength), soil deformation characteristics (such as compressibility and swelling-shrinking property), and soil permeability. The significant carbon sequestration and soil treatment effects of soil biochar depend on its key characteristics, i.e., acidity-alkalinity (alkaline), porosity (porous), adsorption (strong), cation exchange capacity (strong), and carbon stability (high), which are mainly controlled by carbonization materials and carbonization temperature. This study aims to expand the research direction of biochar-mediated soil carbon sequestration coupled with contaminated soil treatment and provide theoretical support for the research and development of collaborative technologies for soil carbon sequestration and soil treatment.</p>