The problem of inter － area frequency support can not be achieved after asynchronous networking is realized through MMC － MTDC． Ｒeferring to the power － frequency characteristics of AC system and the DC voltage droop characteristics of flexible HVDC system，3 frequency coordinated control strategies are designed: fixed frequency control，frequency deviation PI control and power estimation frequency control． Fixed frequency control sets frequency reference value as the constant to obtain power support． The frequency deviation PI control obtains the power support by taking the frequency of converter station with frequency accident and the difference of the average frequency of the coordinated control converter station as the input of PI controller． The power estimation frequency control is based on the instantaneous change of the frequency of AC side of the accident converter station． And the power － frequency characteristic coefficient is used to estimate the power variation to determine the power support of the converter station． In PSCAD simulation software，an asynchronous networking system is set up for simulation verification，and the simulation results show the feasibility and effectiveness of the proposed 3 methods to achieve inter － area frequency coordinated control．