Abstract: The flexibility of quantitative modeling and utilization of multi-energy coupled generation equipment can effectively cope with the impact of renewable energy generation uncertainty on the operation of the power system. For an integrated energy system (IES), an evaluation method of short-term power flexibility is established to evaluate the flexibility of CHP regulation reserve for different ancillary services. Firstly, the heating system model is built, including the heating network's hydraulic, thermal, and thermal load models. Then, considering the flexible release of CHP units at different time scales is affected by different operating boundaries, a thermal output regulation domain model is constructed. According to the characteristics of the multi-source circular network and thermal inertia of buildings, a thermal output regulation domain aggregation model is constructed to evaluate various ancillary service capacities that CHP units reserve. Finally, based on the regulation domain of CHP units, the constraint mechanism between various auxiliary service capacities is analyzed. The capacity of various auxiliary services CHP units provide simultaneously is further evaluated. Simulation analysis is carried out on the 28-node thermal system of Bali island to verify the effectiveness of the proposed method.