With the development of integrated energy system, energy flow analysis of coupling energy network has attracted much attention. In this study, based on the unified energy path theory, energy flow analysis of electricity-heating coupled energy system is implemented considering different time characteristic of each system. Considering the instantaneous change process of heat transfer in the heating system, the dynamic model of heat network is constructed based on unified energy path theory. On this basis, the dynamic models of electric and heating systems are coupled, and the dynamic energy flow calculation method of the coupling system is proposed. Through a case study, the feasibility of the proposed model and calculation method are verified. In addition, the effect of heat source on the dynamic process of heat transfer in the heating system is analyzed.