An integrated energy system (IES) planning method with modular simulation and optimization models is proposed in this paper. A two-layer bus structure is adopted in the simulation model

where the external bus structure is used for power balance while the internal bus structure simulates the fast dynamics of electricity and slow dynamics of heat network in detail. In addition

an improved self-adaptive genetic algorithm (GA) is adopted in the optimization model to solve the multi-dimension and multi-time-scales optimization problem for the regional-user level IEPS. The proposed method can improve the extension flexibility of the system optimal planning model with expected accuracy. A case study is used to verify the effectiveness of the proposed planning method.