When faults occur at the receiving terminal of AC system in AC-DC hybrid power grid， the positive sequence equivalent impedance at the back side is no longer approximately equal to that of the negative sequence， which will bring about adverse influence on existing protection. The operating performance of phase selector device with fault component（PSDFC） at receiving terminal of AC system is discussed in detail. It shows that the difference between positive and negative sequence impedance at inverter side is very evident when PSDFC is used for single phase earthing fault arising in AC-DC hybrid power grid. So the positive sequence current distribution coefficient at both sides is no longer equal to that of negative sequence. As a result， significant fault component difference between the non-fault phases arises and it can lead to the mal-operation of PSDFC. Finally， the correctness of theoretical analysis is verified by experiment data of the real-time digital simulator（RTDS） simulation.