Nowadays,there are many researches on carbon emissions in residential buildings and office buildings at home and abroad,while few studies on carbon emissions in metro construction projects.The carbon emission coefficient method is applied to measure the carbon emission of the metro TBM tunnel and find out its carbon emission characteristics.A system boundary including civil engineering entities,construction equipment,transportation and construction equipment,turnover materials,and labor in the TBM section is established.The research is divided into three stages:building materials and prefabricated components production stage,transportation stage and installation stage.Then the carbon emission factors are defined and selected,and the model of each stage is built,a case study of one TBM section in the Qingdao metro shows that the three-stage carbon emission intensity are 4875.87 tCO2/km,49.54 tCO2/km and 1780.04 tCO2/km respectively,and the total carbon emission intensity is 6705.45 tCO2/km.1.21%to 2.43%carbon emission can be reduced by using recycled building materials through the scenario hypothesis method.