Aiming at the challenges of stochastic fluctuation at both source-load terminals in the optimization operation process of integrated building energy system, considering the influence of source-load uncertainty factors, a day-ahead optimization method for integrated building energy system based on fuzzy chance-constrained programming is proposed. Firstly, based on the equipment model of the integrated building energy system, the day-ahead optimal operation model of the integrated building energy system is established. Secondly, considering the influence of the uncertainty of photovoltaic and electricity, cooling and heat loads in the building system, the uncertainty of source-load is represented in the form of fuzzy chance constraint based on fuzzy membership function, and the day-ahead optimization operation model of building integrated energy system based on fuzzy chance constraint programming is proposed, and the clear equivalence class method is used to transform and solve the model. Finally, the effectiveness of the proposed method are verified by an example analysis.