Abstract Deep exploration of user-side flexibility resources is crucial for large-scale renewable energy consumption. This paper proposed a typical integrated energy system (IES) that comprehensively includes wind power, photovoltaic, thermal power, combined heat and power, hybrid energy storage, and flexible load and constructed the system’s unified power flow model based on the heat current method. On this basis, the regulation capabilities of different typical industrial and residential flexible loads were considered the symmetrical source-type load, which can transfer load and align user demand with the peaks and valleys of renewable energy generation, thus achieving power-energy decoupling. This contributes effectively to renewable energy accommodation capacity when the total electrical energy consumption remains constant. In both typical industrial and residential load scenarios, flexible load reduces integrated costs, increases renewable energy consumption, lowers peak thermal power generation, and decreases the requirement for a battery energy storage system (BESS). Besides, on typical industrial and residential load days, smoothing thermal power generation necessitates 12% and 18% flexible load, respectively, while replacing BESS requires 18% and 23% flexible load, respectively. Therefore, we can obtain the feasible operation ranges of symmetrical source-type load and provide suggestions for configuration capacity design of demand response in integrated energy systems.