The distribution network fault location based on parallel resistance disturbed signal injection is realized by tracking and diagnosing the disturbed signal. It has been widely used in distribution network fault location. However

in practical application

this method has the problem of uncertainty characteristics of the current variation

which causes the fault location device to misjudge. Therefore

this paper establishes the equivalent circuit of the small current grounding system

deeply studies the variation of the fault current after the disturbed signal injected through different non-faulty phases

and analyzes the influence of the load current and the grounding transition resistance. The theory of the effective fault location technology based on parallel resistance disturbed signal is demonstrated. It is proposed that the disturbed signal should be injected through the lagging phase of the fault phase in the ungrounded neutral sysytem or undercompensated arc-supperssion-coil-ground neutral system. The disturbed signal should be injected through the ahead phase of the fault phase in the overcompensated arc-suppression-coil-ground neutral system. The simulation results prove the correctness of the optimization method.