This paper presents an asynchronous distributed global power flow method for transmission-distribution coordinated analysis. Considering the communication delays between the transmission system operator (TSO) and distribution system operators (DSOs), this paper introduces ‘partial synchronization’ instead of full synchronization in the traditional synchronous method. Under this mechanism, the TSO needs not to wait for the slowest DSO to complete its power flow calculation and power injection update before the next iteration can proceed. Numerical experiments demonstrate that the proposed asynchronous method takes less time compared with the synchronous method under the same accuracy requirement. Further, this paper proposes a bi-directional network equivalence method to work against non-instantaneous interruptions. Polynomial fitting is used to describe the characteristics of networks, which enables transmission and distribution networks can independently finish power flow calculation when a non-instantaneous interruption happens. Numerical experiments demonstrate that the proposed method can achieve high accuracy.