Exiting green building assessment standards sometimes cannot work well for large-scale public buildings due to insufficient attention to the operation and maintenance stage. This paper combines the theory of life cycle assessment (LCA) and building information modeling (BIM) technology, thereby proposing a green building assessment method by calculating the greenhouse gas emissions (GGE) of buildings from cradle to grave. Life cycle GGE (LCGGE) can be divided into three parts, including the materialization stage, the operation and maintenance stage, and the demolition stage. Two pieces of BIM software (Revit and Designbuilder) are applied in this study. A museum in Guangdong, China, with a hot summer and warm winter is selected for a case study. The results show that BIM can provide a rich source of needed engineering information for LCA. In addition, the operation and maintenance stage plays the most important role in the GGE reduction of a building throughout the whole life cycle. This research contributes to the knowledge body concerning green buildings and sustainable construction. It helps to achieve the reduction of GGE over the whole life cycle of a building. This is pertinent to contractors, homebuyers, and governments who are constantly seeking ways to achieve a low-carbon economy.