The invention provides a control method and a device for connecting wind power to a flexible HVDC transmission system. Firstly, the actual frequency of an AC grid at a receiving end, the actual frequency of an AC bus bar at a wind farm side, the actual voltage at a DC side of a receiving end converter station are obtained, and the reference voltage at the DC side of the receiving end converter station is determined. Then, the voltage of DC line, the frequency of AC bus and the active power of wind farm are controlled separately, which has high reliability, short frequency modulation response time and good frequency modulation effect. Virtual synchronous machine droop control is adopted in the sending-end converter station, which improves the response speed of frequency regulation and shortens the time of frequency modulation. The frequency of the alternating current bus on the wind farm side is controlled by fixed frequency control or frequency conversion control, The active power of wind farm is controlled by virtual inertia, which makes the increased or decreased power released or supplemented in time when the flexible HVDC system provides frequency modulation for the receiving AC network, and reduces the risk of HVDC line voltage exceeding the limit, and greatly improves the reliability of HVDC system.