At the basic physical architecture and equipment level of the system, the various forms of comprehensive energy systems are basically the same, including the production, transmission, storage and consumption equipment of electricity, heat, cold and gas. This chapter primarily focuses on the integrated energy systems, detailing the digital modeling methods for cold/heat, electricity, and gas coupling, analyzing and optimizing energy flow within the energy network, presenting high-precision and rapid simulation technologies for integrated energy systems, and outling the design concepts and architecture of simulation test platforms. Additionally, an integrated energy system for the transient state of integrated energy was proposed.