The integrated energy system, as a crucial physical form supporting the energy Internet, has rapidly expanded in scale under the continuous wave of technological innovation. The high integration of various energy sources imposes increasingly stringent requirements on the stability and security of system. This paper, set against the backdrop of deliberate attacks, conducts relevant research on the network security of integrated energy system using complex network theory. The study initially focuses on identifying vulnerable links within the integrated energy system. It begins by deriving distribution factors for gas network flow and applies an energy hub to construct a directed weighted topology model for the integrated energy system. Building upon this foundation, the paper introduces maximum flow and information entropy theories, proposing vulnerability identification methods for both lines and nodes. To validate the effectiveness of the proposed model and methods, a system composed of an IEEE-30 node power grid and an improved 11-node medium-pressure gas network is analyzed for vulnerability. The study compares the robustness of typical comprehensive energy systems under different attack strategies, confirming the validity of the proposed model and methods.