The utility model discloses a plug-in type three-dimensional folding iron core of a three-phase transformer. The plug-in type three-dimensional folding iron core comprises three unit folding iron cores which have the same shape and size; each unit folding core is in a shape of an octagonal frame and comprises a left unit iron core column, a right unit iron core column, an upper unit yoke and a lower unit yoke which have the same height; the left end and the right end of the upper unit yoke of each unit folding iron core can be respectively correspondingly mounted on the left unit iron core column and the right unit iron core column by a plug-in manner; each unit folding iron core is formed by respectively embedding a plurality of single folding iron cores which comprise left unit iron core columns, right unit iron core columns, upper unit yokes and lower unit yokes; each unit iron core is manufactured by a silicon steel sheet. According to the plug-in type three-dimensional folding iron core, the upper unit yokes are mounted by the plug-in manner, so that a machine body is integrally assembled, which saves the device input cost and greatly facilitates the assembling of a coil of a three-dimensional transformer.