Abstract: Traditional IF protection schemes is inadequate for AC lines integrated with flexible DC systems and may even result in incorrect operation or failure to operate. To address this issue, a new AC line protection scheme is proposed based on instantaneous inductance parameters. The switching issues of each submodule in the flexible DC converter station are initially analyzed, followed by the construction of the AC line fault model of the DC converter station The instantaneous inductance of AC line ends under different fault locations is calculated based on this model. The calculated value of instantaneous inductance in the case of forward fault is basically consistent with the theoretical value. When an external reverse fault occurs, the calculated value of the instantaneous inductance deviates significantly from the theoretical value. Therefore, a protection criterion is formulated to distinguish internal faults and external faults through the interaction of the logic information at both ends of the two lines. Finally, a hardware-in-the-loop test is simulated in RT-LAB. The results demonstrate that the proposed method’s capability in accurately recognizing internal and external faults. The method runs efficiently and is independent of fault resistance and fault type.