Abstract: Voltage source converter based HVDC（VSC-HVDC） is a future trend for the large-scale offshore wind farms integrate to the grid. Due to fast current vector control of VSC-HVDC receiving-end, offshore wind farms may present no inertial response and become unstable when grid is weak. This paper proposed a novel control strategy for VSC-HVDC system. With the application of inertial synchronization control（INC）, self-synchronization could be realized in receiving end converter（REC） by utilizing the nature response of DC capacitor, while grid frequency could be reflected to DC voltage as well. At the same time, frequency mirroring control was applied in sending end converter（SEC）, with which AC grid frequency could be mirrored to the sending-end instantaneously. Then wind farm could realize inertial response, and REC behaved like a synchronous generator with inertial equivalent to the wind farms and VSC-HVDC system, which largely improved its stability under weak grid condition and frequency supporting ability to the grid. An offshore wind farm with VSC-HVDC transmission test system was modeled in PSCAD/EMTDC software, which proved the validity of proposed control strategy.