In northern China, transmission power system and district heating systems (DHSs) are directly connected by large-capacity combined heat and power (CHP) units, which composes the wide-area integrated power and heat system (IPHS). For better wind power accommodation, it is crucial to explore the operational flexibility of each local DHS in the wide-area IPHS. This paper investigates the available electric flexibility from the DHS through the CHP units and the heat-to-power devices. A flexibility region method is proposed to accurately formulate the DHS’s flexibility in terms of power capacity and energy capacity, with a special emphasis on the temporal-coupling feature which is usually oversimplified in the existing studies. Then, solving algorithm is discussed to construct the polytope-form flexibility region, which provides an explicit and concise description of the electric flexibility from the DHS. Flexibility indicators are also developed for flexibility potential quantification. Further, a practical IPHS dispatch scheme is designed, which performs the wide-area power dispatch and the local-area heat dispatch hierarchically. Numerical simulation demonstrates the effectiveness of the flexibility region method in assessing the DHS’s electric flexibility and performing the IPHS dispatch, as well as the benefit of coordinating the flexibility from multiple DHSs for wide-area wind power accommodation.