Integrated energy system (IES) has become the main development trend of current energy utilization mode with its unique economic, environmental and energy - saving advantages.However, the development of IES is inseparable from the theoretical support of integrated energy simulation system. At present, there are only kinds of mature commercial simulation software for a single energy network on the market. However, the standardized software supporting the joint calculation and analysis of multi - energy flows in IES has not been developed effectively. Regarding the above points,based on the comprehensive model library of integrated energy equipment and networks with the multi- energy of electricity, gas,cooling, heating and steam, B/S structure is applied to build an element-oriented integrated energy online simulation system using Java and Python. The proposed simulation system supports the steady/dynamic simulation of multi - energy flows in energy networks, and can realize the parallel calculation with a high efficiency. Results of the case study simulated in the normal state and fault state are consistent with the theoretical analyses of the operation of networks and equipment, proving that the software system built can be used forthe verification of the operational feasibility of IES planning scheme and realizes the simulation of multi-energy flows under multiple operational states effectively. It has powerful functions and is of practical application value.