Abstract: A line protection method and system for wind farm connected to flexible DC system involves: obtaining high frequency components of voltage and current at protection installations on both sides of a transmission line, when a fault of the transmission line of a direct drive wind field connected to a flexible DC system is monitored; obtaining 1-mode transient action impedance difference of the transmission line, based on the high-frequency components of voltage and current at the protection installations on both sides of the transmission line; determining whether a fault inside the area of the transmission line occurs, based on the 1-mode transient action impedance difference and fault identification criterion of the transmission line, and starting the protection action of the transmission line if it is determined that the fault inside the area of the transmission line occurs.