With the large-scale integration of inverter-interfaced distributed generation (IIDG), the traditional single-power-supply network has transformed into an active distribution network with multi-power-supply and bi-directional power flow, which leads to a decline or even failure in the reliability and sensitivity of traditional distribution network protection methods. To address this issue, this paper proposes a new pilot protection method based on positive sequence fault additional impedance (PSFAI). When an internal fault occurs, the amplitude of PSFAI is close to the transition resistance which is a relatively small value, while the amplitude of PSFAI is theoretically infinitely great during normal operation and external faults. Based on the amplitude characteristic of the PSFAI, a novel pilot protection criterion is constructed to identify the internal faults. Extensive simulation results have demonstrated that the proposed method can accurately identify short-circuit faults, is not affected by the output power of IIDG, and has high sensitivity and ability to withstand transition resistance.