Coupling various forms of energy, such as electricity, gas, cold/heat and other forms of energy, the integrated energy system has realized the cascade utilization of energy, enhanced the comprehensive utilization of energy and the flexibility of energy supply through the energy conversion and resource allocation between its sub-systems. However, the energy flows in different types of energy systems vary in their transmission characteristics, which hinders the unified modeling and overall analysis of the integrated energy system, so it is difficult to achieve and bring into play the overall coordination of the integrated energy system. In this paper, based on the theory of energy network and the axiomatic energy theory, the electrical equivalent model of the transmission line in thermal network and the fluid network are established. Combined with the energy conversion equipment model, the unified modeling of the multi-energy flow systems is completed. Then, taking the minimum total energy loss of the system as the goal, a regional integrated energy system operation optimization model is established, in which the particle swarm optimization algorithm is used to optimize the internal control variables of the system. Finally, an integrated energy system of an island with 32 thermal nodes is modeled and optimized, which verifies the validity of the proposed model and optimization method.