The method determines the structure of an electricity distribution system (1) comprising a substation (2) supplying a set of consumers (5, Ci) via one or more feeders (3, Dj) presenting one or more phases. It comprises the following steps: receipt of first electric consumption information relative to each consumer of the set, receipt of second electric consumption information relative to the feeders or to the phases of each feeder of the substation, use of the first and second information comprising a computing phase to determine consumer subsets, within the set, the consumers of the same subset being supplied by the same given feeder and/or by the same given phase of a given feeder. The device implements this method.