With the continuous development of HVDC technology, the increase in the number of ports in the MTDC system and the increasing complexity of network topology, the deficiency of traditional flow calculation method is becoming clear. In this paper, a power flow calculation method that contains distribution of VSC-MTDC mixed system which based on asynchronous iterative method is put forward. On the basis of the current model converter, by dividing the hybrid system and coordinating calculation of boundary variables, this method achieves the global convergence of the whole system. The shortcomings that numerous converter stations in VSC-MTDC power flow method, slow operations and poor convergence in communication network with large number of nodes, are overcome in this method. Moreover, more control modes in the operation of the converter station are considered. Finally, through the example, the correctness and effectiveness of this method are verified.