Abstract: The existing researches on the state of natural gas pipeline in the reliability evaluation of the electric gas integrated energy system are mostly based on the two-state model of pipelines. However, the actual natural gas pipeline network may have leakage, perforation and fracture after being disturbed. At this time, it can still run for a long time. Therefore, the two-state model is not fully suitable for pipeline fault modeling and analysis. In addition, the calculation of energy supply reliability based on energy flow analysis is large and the calculation efficiency is low. Because the Petri net model can intuitively express the system topology and clearly describe the dynamic transfer process between component states, the direct calculation of system energy flow is avoided and the calculation efficiency is improved in the reasoning calculation of Petri net model based on flow network. Therefore, a novel unified physical network model based on the stochastic Petri net theory was established to evaluate the reliability of the electric-gas integrated energy system. Firstly, a multi-state stochastic Petri net model for component faults was constructed, and the Markov state transfer matrix was solved, and component states were randomly sampled. Secondly, considering the difference of electric and gas transmission speed, the stochastic Petri net model of the system was constructed. According to the rules of inference and calculation, the reliability index of the system was obtained by considering the capacity constraint based on the energy transfer relation and the capacity reduction curve of the pipeline. Finally, two interconnected power systems and natural gas systems were used as examples for simulation analysis to verify the validity of the models and methods.