Waterproof structure of socket connector

The is disclosure is directed to a waterproof structure of a socket connector having a waterproof casing, a socket, a cable and a waterproof plug. A cabling opening is defined on the waterproof cover, a ring step facing to the cabling opening is arranged in the waterproof cover, and the cabling opening is covered by an end cap. The socket is accommodated in the waterproof casing. The cable connects to the socket and passes the wiring opening. The waterproof plug wrapping the cable is arranged in the cabling opening to close the cabling opening, the waterproof plug has an inner end and an outer end, the inner end is arranged toward the socket, and a longitudinal annular rib is arranged on the inner end. The end cover is fastened to the waterproof casing to press the outer end, so that the longitudinal ring rib presses the ring step surface.