In order to cope with the new development stage of building green renovation, the green renovation of existing public buildings has also put forward new requirements accordingly. The envelope structure is an important part of the building resistance to the external environment, and its green performance directly affects the building use performance and to some extent the building use experience. The higher the comprehensive green performance of the envelope of existing public buildings, the lower the energy consumption and the stronger the greenness of the building as a whole, so the envelope is a key research object in the green renovation of existing buildings. This paper mainly discusses the common envelope insulation system and technology in the green renovation of existing public buildings and analyzes its suitability, in order to provide some technical reference for the actual green renovation of existing public buildings.