Abstract: Based on the life cycle theory of carbon emission of deep foundation pit engineering, a green technology demonstration building project in Shanghai is taken as the background, and the carbon emissions of the foundation pit during life cycle of the all-steel low-carbon support scheme composed of PC method combined steel pipe pile enclosure and prestressed steel composite support and the conventional concrete support scheme are quantitatively calculates and compared. The research results show that the total carbon emissions of the foundation pit during life cycle of the all-steel support system is 21% of that of the concrete support system. The carbon emissions of the all-steel support system can be further reduced by increasing the number of reuses, selecting low-energy consumption machinery, and shortening the transportation distance, etc.