Abstract: A magnesium oxide-based steel pipe carbonization composite pile (MSCP) is proposed. The steel pipe mixing core serves as both an inner pile and a gas injection channel, therefore a composite pile with the outer serpentine-magnesium oxide mixing pile can be carbonized. Based on the research methodology that integrates full-scale field tests and comprehensive benefit evaluation, mechanical experiments including standard penetration tests, unconfined compressive strength tests, and static vertical compressive load tests are conducted, combined with machine-hour statistics and life cycle assessment. The study aims to investigate the quality and bearing characteristics, and to comparatively evaluate construction cost and carbon emissions. The results indicate that MSCP can be carbonated rapidly during CO₂ injection, with the strength and stiffness of outer pile core significantly improved compared to foundation soil. The inner and outer pile core jointly share the vertical load; the inner pile limits compressive deformation and delays crushing failure of the outer pile, while the outer pile facilitates load distribution through lateral friction resistance. Meanwhile, compared with traditional pile types, MSCP demonstrates better cost-effectiveness and low-carbon advantages. In summary, MSCP is a novel fast-hardening, high strength, and eco-friendly and carbon-sequestration composite pile.