Based on the life cycle assessment perspective of the project, this paper establishes the Multidimensional Information Model of the green building, quantifies the environmental Impact of buildings, defines the effect of the choice of the green building technology on the carbon emission reduction of the project and adopts a benchmarking project to establish benchmarking projects. Taking the design scheme of a primary school teaching building in Changsha as an example, the model is established and calculated. Based on the calculation results, the effects of different green technologies on building carbon emissions in different stages of the whole life cycle of construction projects are analyzed. Using the same method, the carbon emission reduction and individual advantage weights of other projects in different stages of the whole life cycle are obtained to select the individual benchmarking and group benchmarking for each green building project.