Abstract: The power system is an important infrastructure of modern society and one of the main sources of carbon emissions, and accurate and fair measurement of carbon emissions is the foundation and prerequisite for the power industry and power users to realize emission reduction targets. In order to realize the carbon emission accounting of regional distribution networks, and then provide a reference basis for the verification of carbon emission and energy saving and carbon reduction of the power system, an indirect carbon emission calculation method for regional distribution networks is proposed based on the line power composition analysis method of graph theory. Firstly, based on the transmission relationship among power source, load and line, the regional characteristics of the power system and carbon emission responsibility sharing are clarified. Then, the carbon emission contribution factor is determined based on the graph theoretic sequential trend tracking method, and the carbon emission among source, network and load is calculated. Finally, the carbon flow tracking method is used to realize the carbon emission sharing of contact line and branch loss, and the simulation calculation is carried out with 2-machine 4-node system and IEEE-14-node system as an example, which verifies the validity of the proposed sharing method. The results show that the proposed indirect carbon emission calculation method based on graph theory is characterized by clear principles and fast calculation compared with the traditional method, and the calculation rate is improved by about 30% under the premise of guaranteeing the calculation accuracy.