Electricity and heat are used as secondary energy sources and the carbon emissions generated by the heating and power supply systems basically come from the capacity side. At the same time, with the development of integrated energy sources, the coupling of electricity and heat networks has become tight. Therefore, how to define the responsibility for carbon emissions on the capacity, transmission and user side to measure carbon emissions is an important measure to promote low-carbon development in all parts of the electricity and heat networks. In this paper, to address this issue and to improve the limitations of existing macro-metering, a whole-flow carbon metering method based on carbon emission streams for coupled electric and thermal networks considering network losses is proposed. Firstly, the definition and index of carbon emission flow in electric and thermal networks are proposed, and the carbon emission flow model of electric and thermal coupling networks as well as coupling equipment is established. A carbon emission measurement method involving the whole flow of energy transmission is proposed. The calculation method of carbon emission flow is proposed according to the characteristics of the model, finally an example system is given to verify the accuracy of the model and algorithm.