With the rapid development of distributed power supply in distribution network, the coupling between provincial and local power grids has been greatly enhanced. An asynchronous power flow calculation method for provincial-local coordinated operation is proposed. Considering the communication delays between provincial and local dispatching centers, this paper introduces the concept of “partial synchronization” to replace the traditional synchronous provincial-local power flow calculation. Furthermore, a historical-data-based equivalent method for distribution networks is proposed. When non-instantaneous interruptions occur between provincial and one local dispatching center, the provincial dispatching center can establish an approximate model of this distribution network based on the historical data received from the local dispatching center. Polynomial fitting is used to establish a surrogate function between boundary nodal power injections and nodal voltages, and the provincial dispatching center can independently accomplish transmission power flow calculation with the surrogate function under communication interruptions. Numerical experiments show that the proposed asynchronous method can achieve the same accuracy compared to the traditional method and significantly improve efficiency. Also, the proposed surrogate model can satisfy the accuracy requirements.