An improved transformer structure mainly has a lower iron core disposed with a plastic securing seat having a central insert tube provided for the insertion of circular posts disposed respectively on an upper and the lower iron cores; a plurality of pins on the lateral sides of the plastic securing seat respectively provided for the fixing insertion of through holes on a circuit board thereby fastening a flat coil and the circuit board on the plastic securing seat so as to increase the pressure resistance value of the iron cores and the coil as well as obtain a precise positioning point of the transformer and level the pins meet the standards of Storage Module Device (SMD).