Park-level integrated energy system, as a energy coupling component of urban energy systems, plays a great role in promoting various types of energy coupling. Traditional planning method of park-level integrated energy system does not allocate reasonable equipment capacity according to the difference of load level in different time sequence stages, resulting in redundancy at the initial stage and shortage at the final stage. In this paper, based on the concept of multi-stage planning, a multi-stage equipment capacity configuration planning model of park-level integrated energy system including electricity, gas and heat is proposed, the objective function of which includes cost of investment, operation, maintenance and compensation. On this basis, the influence of thermal flexible loads caused by the transmission delay of heat supply network and the ambiguity of user’s temperature perception, as well as the influence of electrical flexible loads such as shiftable load, transferable load and curtailable load on equipment capacity configuration are considered. The simulation results show that the idea of multi-stage planning can reduce equipment capacity configured in the preliminary stage and increase equipment capacity configured in the later stage, which conforms to the change law of load level. The introduction of flexible loads can reduce the amount of equipment capacity configured in each stage without destroying the balance between energy supply capacity and load level by optimizing the load curve structure.