Abstract: A multi-port PV DC boost collection grid-connected system has many branches, short lines, fast fault development and high current peak, and it is difficult to identify the fault section quickly and reliably. In order to realize rapid fault isolation and recovery of the system, an inter-electrode fault segment identification method based on the relative phase of high frequency current is proposed. Firstly, the transient equivalent network is constructed after faults in different segments, the equivalent parallel capacitor and current limiting inductor are used to simplify the equivalent network, and the correlation characteristics between high frequency currents are obtained. Then, the correlation is quantified as phase difference distribution, and the fault section identification criterion is constructed based on the phase difference distribution between the collector branch and the sending line. The identification result is output in the form of logical quantity. Finally, the simulation results show that the method can be adopted to reliably select the line within 2ms after the fault at the earliest, and has strong resistance to noise, transition resistance, and distributed capacitance. The method is simple and practical, and has a certain engineering application value.