A dedicated plug capable of preventing external connection of internal networks of computers achieves distinguish and separation between internal network cables and external network cables and between internal network computers and external network computers and completely avoids unintentional irregular external connection events. The dedicated plug comprises a cable and is characterized in that the cable is divided into an A section and a B section. The A section of the cable is a long cable and applied to long-distance connection, a cable sequence of the A section of the cable is a non-568B cable sequence, and a pressing piece of an external connection plug of the A section of the cable is a semi pressing piece and used for locking a wall or a router end. The B section of the cable is a short cable, a cable sequence of the B section of the cable is a 568 cable sequence, a pressing piece of an external connection plug of the B section of the cable is a semi pressing piece and used for locking a computer end, and a warning sign saying cable only for internal network computer and no plugging is adhered to the external connection plug of the B section of the cable. The A section and the B section of the cable are connected through connectors, and a cable sequence converting circuit is arranged on the connector of the B section of the cable.