The rapid economic development and the problem of carbon dioxide outputs are becoming more and more serious. Based on the fact that the research on carbon dioxide output of fabricated steel structure buildings is at the initial stage, this paper establishes relevant carbon dioxide output calculation models by studying the carbon dioxide output calculation methods of fabricated steel structure buildings in the construction stage. The results show that: for steel structure stadiums and gymnasiums, (1) steel components and their accessories play a leading role in the carbon dioxide outputs of the main materials, (2) in the resources consumed in the process of realizing materialization, the carbon dioxide outputs produced by electricity occupy the first place, followed by welding wire and flux. The research results in this paper can be used to support the carbon dioxide output calculation of other relevant buildings, and also have certain guiding significance for assessing the carbon dioxide output reduction potential of steel structures.