The fault currents on both sides of the AC submarine cable line of the MMC-HVDC system of offshore wind power are controlled, the fault characteristics are obviously different from the traditional synchronous power supply, and the differential protection has the risk of incorrect action. To solve this problem, an AC submarine cable pilot protection for offshore wind power through the MMC-HVDC system based on mean absolute error is introduced in this paper. The proposed protection constitutes a protection criterion according to the difference of the calculated mean absolute error between the current sampling value on one side and the current sampling value on the other side in a certain time window, and the performance of the proposed protection is analyzed. PSCAD software is used to simulate and verify the effectiveness of the proposed protection under various working conditions. The simulation results show that the proposed protection can act correctly in case of faults inside and outside the area, and has good performance in case of high resistance fault. It can also work normally in the face of the extreme case of no output of the fan and has the function of phase selection. Its performance is superior to the differential protection, which is more suitable for the AC submarine cable line of offshore wind power through the MMC-HVDC system.