The transportation sector is responsible for about 24% of global greenhouse gas emissions. Controlling the carbon emissions from the transportation sector is of great significance to achieve carbon neutrality. Based on analyzing the carbon emission process of various transportation modes, this paper analyzes the influencing factors of carbon emission factors of different transportation modes. Through the calculation model of carbon emission factors of different transportation modes, the size of carbon emission factors of various modes is analyzed. The research showed that the carbon emission factor of air transport is significantly higher than other modes of transport, followed by road, railway and water transport. Compared with the United States, the carbon emission factors of passenger transportation and freight transportation in China are all lower than those in the United States except air freight, China′s railway transport density is 4.4 times than that of the United States, and the carbon emission factor of freight and passenger transport is 50% and 81.56% of that of the United States.