The invention discloses a single-phase earth fault ranging method based on a distribution automation system. The method includes the steps of collecting zero-sequence voltage and zero-sequence current at the two ends of a distribution line, judging the calculation state according to the zero-sequence voltage and zero-sequence current at the two ends of the distribution line, and calculating fault points of the distribution line according to a line distribution parameter circuit model when the zero-sequence voltage and zero-sequence current at the two ends of the distribution line are detected, when three-phase current and voltage are detected at one end of the distribution line and zero-sequence voltage and zero-sequence current are detected at the other end of the power distribution line and when three-phase current and voltage are detected at one end of the distribution line and no current or voltage is detected at the other end of the distribution line. Application conditions for application of power distribution networks are given through a single-phase earth fault point positioning method; fault ranging conducted under the three conditions is achieved by capturing zero-sequence voltage and zero-sequence current generated instantly when one-phase earthing happens; according to the single-phase earth fault ranging principle based on the line distribution parameter circuit model, only distribution terminals need to be assembled at a main line node and important branch nodes to collect zero-sequence voltage and zero-sequence current of the line.