Abstract: As a basic application of energy network analysis, different energy networks have developed fully-fledged but not unified models and methods for energy flow calculation. To improve the disciplinary integration of different energy network research, an energy flow calculation method based on the energy-circuit theory was proposed for natural gas networks and heating networks. In addition, an iteration method for correcting base value was supplemented to improve accuracy, and an equivalent method from boundary conditions to initial conditions was employed to set initial conditions in an implicit manner. The proposed method unifies not only energy flow calculations in different energy networks, but the steady and the dynamic energy flow calculations, which establishes the basis for the multi-time-scale integrated analysis of heterogeneous energy flows. Furthermore, the proposed method outperforms the conventional energy flow calculation methods in terms of computational performance.