Abstract: In allusion to the problem of low sensitivity and poor reliability of existing selective leakage protection device, the paper proposed a line selection method of selective leakage protection based on characteristic quantity of zero-sequence current. It analyzed logical relationship of zero-sequence current of each branch during failure of power supply system and introduced principle and realization of the method. The method creates characteristic quantities according to logical relationship and value relationship of secondary side zero-sequence current of zero-sequence current transformer of each branch, and takes the characteristic quantities as criterion of line selection. Matlab simulation result showed the method can effectively select the fault line.