Abstract: A combinational universal serial bus (USB) transmission structure mainly includes a control unit consisting of at least a USB interface and a driving IC. The control unit is provided with an I/O connector, which may be connected to or replaced with a corresponding I/O connector provided on, for example, a flash memory module, a card reader module, a hub module, and/or other externally connected expansion modules. Therefore, when the control unit is to be used in different functional conditions, it may be connected to or replaced with different expansion modules via the I/O connectors to achieve multiple functions and reduce the manufacturing cost for the USB transmission structure.