Abstract: Load fluctuation is rarely considered in the planning of integrated natural gas and electric power systems. The reason is that the boundary of information condition is not clear and the applicability of planning model is low for lack of measurement data. Based on this, a multi-objective expansion planning model for transmission level integrated energy system based on information gap decision theory(IGDT) is proposed. Firstly, based on the multi-objective expansion planning model, the uncertainty sets of the maximum fluctuation range of electric and natural gas loads are described. Secondly, the information gap decision theory is used to quantify the level of uncertain factors in typical scenarios, and the optimization margin of the planning model is expanded through transmission switching. Finally, the improved epsilon-constrained algorithm is adopted to solve the multi-objective expansion planning model, and the optimal planning scheme under the pareto solution set is determined by fuzzy decision-making. The simulation results of IEEE-RTS 24 node system and Belgium 20 node system show that the proposed model can effectively quantify the impact of multiple coupling uncertainties in the integrated energy system load, and transmission switching can effectively enhance the planning optimization space.