The rail transit construction process produces a large quantity of carbon emission. The carbon emission could be divided into two sources, including direct carbon emission from the construction process and indirect carbon emission by raw material utilization. With the promotion of China National carbon peaking and carbon neutrality goals, it is an industry trend for the rail transit construction company to reduce carbon emission during the construction event. This study provides a detailed overview of the possible carbon emission process and carbon mitigation process during the rail transit construction event and puts forward preliminary carbon mitigation suggestions and strategy for the rail transit construction process. The predominant carbon emission section during rail transit construction is the raw material (including the steel, cement, concrete, tunnel segment), electricity, and fuel consumption during construction. It is suggested that the rail transit construction process could achieve carbon emission mitigation from the following prospects: make careful plans for the raw material selection (such as using recycled concrete, recycled steel, and so forth), improve the construction process to reduce energy waste, and optimize the equipment selection during the mechanical and electrical installment process. By this, the carbon emission could be mitigated during the rail transit construction.