Abstract: District heating networks exhibit considerable energy storage potential due to their thermal inertia, enabling sufficient operational flexibility for power systems. However, the complex energy transfer characteristics and data privacy concerns of heating networks pose great challenges to the accurate evaluation of their storage capability. To address this issue, an approximate model considering dynamic properties of heating networks is proposed to aggregate the storage capacity of heating networks. First, the flexibility of the heating network is modeled as a physically meaningful equivalent energy storage model to quantify the thermal storage capacity of pipelines. Building upon this, the basic polyhedron translation and scaling method is employed to determine the parameters of the heating network equivalent energy storage model. Furthermore, the proposed flexibility aggregation model is applied to the coordinated optimization of integrated electricity-thermal energy systems, and numerical simulations are conducted for validation. Simulation results demonstrate that the proposed aggregation model can solve the combined power-heat dispatch problem non-iteratively while avoiding the detailed heating network modeling required by conventional centralized approaches. Meanwhile, the optimized results can maintain a high level of computational accuracy.