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The invention relates to a power distribution network fault line selection method based on a variable-scale bi-stable system. The method comprises steps as follows: firstly, after a distribution network has a single-phase earth fault, transient-state zero-sequence current izn(t) from one cycle before the fault to one cycle after the fault of each branch line is selected; then parameters a and b of a potential function in the variable-scale bi-stable system as well as numerical values of a four-order Runge-Kutta equation are set for calculation of step length hs; then the izn(t) is transformed correspondingly according to the amplitude of the izn(t), the transformed izn(t) replaces s(t) in an expression of the variable-scale bi-stable system, the four-order Runge-Kutta equation is used for solving, and the obtained solution is an overall feature signal isn(t); then data, from 0.02 s to 0.025 s, of the overall feature signal isn(t) are selected as feature current; finally, distribution network fault line selection is performed by the aid of plus-minus signs of cross correlation coefficients of the feature current of all lines: if signs of the cross correlation coefficients of a certain line are identical, minus 1 is output, and the line is judged as a fault line; if signs of the cross correlation coefficients of a certain line are different, 1 is output, and the line is judged as a non-fault line.