Abstract: The construction industry of our country has entered a new period of stock improvement and urban renewal, and it is helpful to explore the calculation methods of building carbon emission from the renovation of existing public buildings. Based on the characteristics of existing public building renovation, this paper determined the boundary conditions for carbon emission calculation, adopted the carbon emission factor method to establish the carbon emission calculation model of existing public building renovation, verified the carbon emission calculation method of existing public building renovation through project cases, analyzed and discussed the carbon emission factors affecting the building renovation, and provided data basis for carbon reduction of existing public building renovation. It provides a reference for promoting the development of architectural transformation and the green and low-carbon construction of urban renewal.