This chapter integrated the theories of analytical mechanics, thermodynamics, electrical network, fluid network, and other disciplines to construct an energy network theory grounded in axiomatic thinking. The unified energy network model applicable to typical integrated energy systems was developed. Drawing on electrical network theory, the unified energy network equation for integrated energy systems and its solution methodology were established. Furthermore, the network equation for a simplified integrated energy system was formulated and simulated, thereby validating the effectiveness and practicality of the proposed model and approach.