By adopting John W.Creswell's five-step method of literature review,this study combed related papers in the framework of concept,method and research content.It was found that the connotation of carbon emissions could be either CO_2-e or CO_2.The calculation of them mainly followed the line of up-bottom and bottom-up,which usually used the method of carbon emission index,and both methods had strengths and weaknesses.The research content included three parts,including the importance of carbon emissions by tou...