Abstract: Power system is one of the main sources of carbon emissions in China, and accurate and fair carbon emission accounting and carbon burden sharing are important prerequisites for promoting low-carbon transformation of the power system. The traditional carbon emission flow calculation method is insufficiently applicable in lossy networks since it ignores network losses. The existing network loss carbon emission apportionment methods have shortcomings such as the overly rough network loss apportionment and the apportionment process leading to the complexity of the network structure. To this end, a carbon emission flow calculation method of the power system that considers network losses is proposed under the condition of no change in the network structure. The method realizes the conversion from lossy network to equivalent lossless network by calculating the equivalent net output of each unit at the source side and the equivalent transmission power of the line, and apportioning the network loss to the source side. Based on the results of network loss sharing, the key matrices and vectors required for carbon emission flow calculation are further modified, and the carbon emission flow calculation method of lossy network is proposed. The case analysis uses 4-node and 30-node systems to verify the effectiveness of the above method, and the results show that the proposed method can quantify the carbon flow distribution on each side of the source-network-load of the lossy network.