Global climate change necessitates urgent carbon reduction, with the building sector being a major contributor. This study conducts a comprehensive life cycle carbon emission analysis of a nearly zero-energy office building in Shenyang, China, using the LCA theory and the carbon emission factor method. The calculation covers the production and transportation of building materials, construction, operation, and demolition stages. The results show that the building’s average annual carbon emission intensity is 56.36 kgCO₂e/(m²·a). The operation stage contributes the largest share, with an intensity of 37.83 kgCO₂e/(m²·a), primarily due to HVAC energy consumption. The material production and transportation stage follows, accounting for 31.67% of total emissions. Compared to conventional buildings, the proportion of operational emissions in this nearly zero-energy building is relatively lower, while the share from material production is significantly higher due to the use of high-performance insulation and components. Based on these findings, targeted carbon reduction strategies are proposed for each life cycle stage, emphasizing low-carbon material selection, renewable energy utilization, and efficient design. This study provides a quantitative reference for achieving carbon reduction goals in the building sector.