As one of the world’s primary sources of carbon emissions, the building sector’s decarbonization progress directly affects the realization of “dual carbon” goals. Based on life cycle theory, this paper systematically analyzes the technical logic and limitations of carbon emission accounting methods for buildings, and elaborates on innovative pathways for green building decarbonization technologies, including passive design, active energy systems, and BIM-based digitalization. The Technology Acceptance Model (TAM) and a tripartite evolutionary game framework are introduced to analyze the barriers and driving mechanisms for technology diffusion from a socio-technical perspective. Using practical cases from China Construction Science and Technology Group Co., Ltd. (CSCSTC), the paper quantifies emission reduction performance. Finally, a coordinated implementation framework integrating policy regulation, technological innovation, and market incentives is proposed. Results show that combining Life Cycle Assessment (LCA) with the emission factor method can improve accounting accuracy by over 30%; integrating passive design and renewable energy technologies reduces building energy consumption by 50–64%; and scaled application of the “Photovoltaics + Energy storage + Direct current + Flexibility” (PEDF) system achieves renewable energy self-consumption rates above 80%. Furthermore, modular construction reduces carbon emissions from the construction phase by 30%, while green financial instruments such as preferential loans can raise project internal rates of return (IRR) by approximately 2–3 percentage points. This study provides theoretical support and practical guidance for low-carbon transition in the building industry.