A combined structure of a USB plug with a built-in card-reading slot, and more particular, a combined structure for the patent application U.S. Pat. No. 7,575,481 that permit a convenient manufacturing and meets different needs. An isolation base is provided in cooperation with two or three different isolation pieces which are joined by a hooked connection to create a module. The isolation pieces are each provided with an engaging slot. It is possible to choose the desired terminal set of certain type to achieve the predetermined functions of a certain USB specification. A metal housing meeting the specification of USB A-type plug dimensions encloses the compound connection module, thereby creating a first slot for the electric connection with the female connector of USB 2.0 or USB 3.0. Meanwhile, a second slot is provided for the insertion of the thin-type Micro SD/T-Flash memory card. Accordingly, a USB plug with a built-in card-reading slot is created. Moreover, the USB plug is an independent connection element that allows for a convenient connection with circuit boards or electronic products having different functions. As a result, the requirements of different electronic products are fulfilled.