A butterfly interface transfer structure including an interface card, a first add-in card and a second add-in card is disclosed. The interface card includes a plate, a first connector, a second connector and a spacer. The plate has a set of electrical connecting pins, a first surface and a second surface. The first connector is disposed on the first surface, and the second connector is disposed on the second surface, wherein the first connector and the second connector are respectively electrically connected to the electrical connecting pins. The spacer is disposed between the first connector and the plate. The first add-in card is coupled to the first connector, and the second add-in card is coupled to the second connector.