Abstract: With the access of distributed generation to low-voltage distribution network, the power flow of the distribution network becomes more complicated. As a result, the traditional fault location scheme based on one-way power flow no longer applies. This paper proposes a perturbation based phase-mode transformation to achieve the fault location for low-voltage distribution networks with distributed generation. Against the asymmetry of three-phase line parameters in low-voltage distribution network, the line parameter impedance matrix perturbation is constructed with the perturbation theory to derive the phase mode transformation matrix which can decouple the original three-phase networks into three mutually independent sequence graphs, consequently realizing the decoupling of the parameter impedance matrix of asymmetric lines. And then, A criterion is derived for judging the fault section of the low-voltage active distribution network according to the changes of the fault component phase angle differences of the section phase-mode transformation current before and after the fault, realizing the accurate position of the low voltage distribution network. The Matlab/Simulink simulation results show that the proposed method can quickly and accurately locate the fault section and solves the influence of the asymmetry of distribution network parameters on positioning accuracy.