A coupling structure of a cable connector, comprising: a first connection head including a first joint part, a plurality of insertion terminals disposed in the first joint part, and an external threaded portion formed on an outer peripheral surface of the first joint part; and a second connection head including a second joint part, a plurality of insertion holes disposed in the second joint part, a fastening sleeve surroundingly disposed outside the second joint part, a socket formed between the fastening sleeve and the second joint part, a positioning ring receiving the fastening sleeve, a plurality of fastening elements arranged spaced apart from each other between the positioning ring and the fastening sleeve, and a quick-release fastening ring detachably fastening the fastening elements, wherein the first joint part is inserted into the socket, the insertion terminals are correspondingly inserted into the respective insertion holes, the quick-release fastening ring rotatably presses on the fastening elements, an internal threaded portion of each fastening element is engaged with the external threaded portion of the first joint part, a plurality of pressing portions spaced apart from each other protrude from an inner surface of the quick-release fastening ring, the fastening elements are disposed corresponding to the pressing portions respectively, each fastening element includes an inclined surface and a protruding portion connected to the inclined surface, each pressing portion is rotated to press from each inclined surface onto each protruding portion, the fastening sleeve includes a plurality of fastening holes for accommodating the fastening elements respectively, and the positioning ring includes two connection strips to limit movement of each fastening element and includes a plurality of connection plates connected to the connection strips; characterised in that two sheet portions protrude from two side edges of each fastening element respectively along a direction of each connection strip, and the fastening sleeve includes two recesses arranged corresponding to the two sheet portions respectively. a first connection head including a first joint part, a plurality of insertion terminals disposed in the first joint part, and an external threaded portion formed on an outer peripheral surface of the first joint part; and a second connection head including a second joint part, a plurality of insertion holes disposed in the second joint part, a fastening sleeve surroundingly disposed outside the second joint part, a socket formed between the fastening sleeve and the second joint part, a positioning ring receiving the fastening sleeve, a plurality of fastening elements arranged spaced apart from each other between the positioning ring and the fastening sleeve, and a quick-release fastening ring detachably fastening the fastening elements, wherein the first joint part is inserted into the socket, the insertion terminals are correspondingly inserted into the respective insertion holes, the quick-release fastening ring rotatably presses on the fastening elements, an internal threaded portion of each fastening element is engaged with the external threaded portion of the first joint part, a plurality of pressing portions spaced apart from each other protrude from an inner surface of the quick-release fastening ring, the fastening elements are disposed corresponding to the pressing portions respectively, each fastening element includes an inclined surface and a protruding portion connected to the inclined surface, each pressing portion is rotated to press from each inclined surface onto each protruding portion, the fastening sleeve includes a plurality of fastening holes for accommodating the fastening elements respectively, and the positioning ring includes two connection strips to limit movement of each fastening element and includes a plurality of connection plates connected to the connection strips; characterised in that two sheet portions protrude from two side edges of each fastening element respectively along a direction of each connection strip, and the fastening sleeve includes two recesses arranged corresponding to the two sheet portions respectively.