Abstract: When a fault occurs on the MMC-transmitted AC line of offshore wind power, the phase and amplitude of the fault current are affected by the control strategies of the converters on both sides. Aiming at the problem of the operation failure of existing ground distance protection, an MMC-side distance protection scheme for single-phase-to-ground faults on offshore wind power AC lines based on adaptive phase compensation of additional impedance is proposed. First, based on the composite sequence network of the single-phase-to-ground fault on the MMC-transmitted offshore wind power AC line, the mathematical relationship between the fault current and the sequence currents on the MMC-side is derived, and the adaptive phase compensation coefficient of the additional impedance for the MMC-side ground distance protection relay is constructed. Then, the adaptively compensated measured impedance and the line impedance on the MMC-side are calculated, the imaginary part of the grounding impedance is solved, and thereby the fault distance is calculated. This method compensates for the influence of the control system on the fault current, eliminates the impact of the fault resistance on the distance protection, and achieves the accurate calculation of the fault location. Finally, a simulation case model is built in the PSCAD/EMTDC electromagnetic transient simulation platform. Test results show that this method can accurately identify internal and external faults and has a strong tolerance to fault resistance.