Abstract: Aiming at the security analysis of natural gas network in the integrated energy system（IES）, a security region model of natural gas network is proposed, which is based on the unified modeling method of heterogeneous energy. Firstly, the basic concepts about the security region of natural gas network are presented. Secondly, the unified modeling method, which is suitable for the comprehensive analysis of heterogeneous energy networks, is introduced. It is shown as the gas circuit model in the natural gas network. Therefore, the steady-state model of gas circuit is established first, and the steady-state model of security region based on the gas circuit is established further, which means the mathematical form of natural gas network and electric power network is unified in the security region. Thirdly, the methods of full-dimension calculation and reduced-dimension observation of the above model are proposed. Finally, verification is carried out on a typical 5-bus case and an actual Belgium gas network system.Compared with the traditional security region model based on the pressure drop equations, the proposed model and method can significantly improve the calculation efficiency on the premise of correctness and accuracy, which lays the foundation for the subsequent general modeling and analysis of the security region of the integrated energy system.