Abstract: Due to the introduce of the inverter interfaced distributed generations (IIDG), the original protection of the distribution network has been changed. Based on the ratio between the sum of two terminals positive sequence voltage phasor of the transmission line and the sum of two terminals positive sequence current phasor of the same line, which is defined as positive sequence summation quotient impedance, a new positive sequence line pilot protection principle is proposed. When an outer fault occurs, the positive sequence summation quotient impedance reflects the capacitance impedance of the line, and its value is large. When an internal fault occurs, if the line impedance is ignored, the ratioreflects 2 times the transition resistance or 4 times the transition resistance, and its value is relative small. When the faults occurs in outer or internal, the amplitude of the positive sequence component integrated impedance varies obviously and therefore, the internal and outer faults on the line can be distinguished. Simulative results show the new principle has strong resistance to transition resistance and obvious characteristics and is easy to tun and is not affected by the control strategy and the generated power of the distributed power supply.