The invention discloses an online distribution line fault waveform acquisition method, which belongs to the detection field. A fault indicator is arranged on each of three phases of lines of a plurality of towers along a distribution network overhead line; the tower of the fault indicator is provided with a monitoring communication terminal; short-distance wireless communication networks are arranged among the three fault indicators and between the fault indicators and the monitoring communication terminals on the same towers; and the monitoring communication terminals and a system master station perform long-distance wireless network connection through a GPRS wireless network. Fault data for fault current in each section of line are acquired synchronously through the fault indicator, a three-phase current waveform at the fault moment can be reproduced, zero-sequence voltage and current can be calculated through a protection algorithm, grounding fault is judged auxiliarily, and the grounding fault judgment accuracy is greatly improved. The technical scheme of the invention is particularly suitable for a small and medium-sized city distribution network automatic construction mode or a large-sized city distribution network automatic reconstruction supplementary project.