Abstract: The capacitance per unit length of a cable is 20 times more than that of an overhead line at the same voltage level, and more and more offshore wind power is connected to the grid through AC cable, which reduces the natural resonant frequency of the transmission system and increases the resonant risk of the system. Aiming at the resonant overvoltage phenomenon in the process of grid connection of an offshore wind farm, the fault recording data are analyzed. Based on the impedance model of the transmission system, the mechanism is analyzed, and through the electromagnetic transient simulation, it is verified that the natural resonant frequency near the double frequency of the transmission system is the fundamental reason for the resonant overvoltage caused by the closing operation of no-load transformer and no-load line in the wind farm. Combined with the engineering practice, the joint suppression measures of changing the operation mode of the transmission system, optimizing the control and protection system of the static var generator and increasing the access load are proposed. Finally, the effectiveness of the proposed measures is verified by simulation and field tests.