With the early construction and prolonged use of buildings, energy systems have gradually exposed issues such as single configuration, insufficient system capacity, and environmental unfriendliness. To address these issues, it’s necessary to undertake expansion planning for a building integrated energy system. Firstly, basic equipment models of a building are established, and a carbon cost mechanism is used to restrict carbon emissions during the planning process. Then, based on this, a bi-level model for building integrated energy system expansion planning is established. The upper layer is the capacity planning stage to minimize the equipment investment costs, and the lower layer is the operation optimization stage to minimize the sum of the system operating costs and the carbon costs. Finally, using a two-stage robust planning approach to address load uncertainty, where the uncertainty is characterized by upper and lower bound interval estimates, consequently establishing a robust planning model. To demonstrate the effectiveness of the planning approach, an example is presented, focusing on its efficiency and carbon reduction capabilities.