The power-gas-coupling can realize the cascade utilization of energy in the integrated energy system, which is conducive to improving the utilization of energy and reducing pollution gases emissions. With the installation of smart metering, two-way communication between suppliers and consumers is feasible, which enables the implementation of demand response. A generic optimal planning model is proposed to assess the economic and environmental benefits of the capacity allocation of the grid-connected integrated energy system considering both price-based demand response and incentive-based demand response respectively. The optimal planning problem is formulated as a mixed-integer linear programming model with the objective to minimize the total annual cost. The results from three configuration modes are compared in the case study, which illustrate the economic and environmental benefits from demand response. In addition, the impact of the sales capacity constraint on the grid and the fluctuation of electricity and gas prices on the planning of the integrated energy system are also extensively studied considering demand response.