The coordinated operation of an integrated energy system (IES) and a distribution network is the inevitable development trend of the energy Internet of the future. The day-ahead optimal scheduling of the IES is an important way to improve new energy efficiency and the energy economy. When the IES and the distribution network exchange electrical energy, the voltage of the distribution network may be out of limit. This article presents a two-stage joint optimal scheduling method for a distribution network with IESs to improve the economy of the IESs and the safety of the distribution network. In the first stage, the user's demand response and the electrical energy interaction between IESs are considered, and the schedulable potential of the systems is fully tapped. In the second stage, a bi-level scheduling model is adopted: the upper model takes the distribution network as the control object and reduces the power loss by adjusting the exchange power between the distribution network and the IESs. The lower model takes the IESs as the control objects and obtains the scheme with the lowest cost in each IES through multi-objective particle swarm optimization. Taking the IEEE 33-node distribution system as an example, simulation research is performed to show that the total network loss is 17.01% lower and the total cost is 5.36% lower than the method without two-stage optimal scheduling, which verifies the effectiveness of the proposed method. INDEX TERMS Integrated energy system (IES), joint optimal scheduling, power interaction, bi-level scheduling model.