The utility model discloses a moistureproof connecting structure of an underground cable. The cable connector comprises a connecting piece and an inner shell, the first connecting piece is composed ofan outer shell and an inserting piece, the inner shell and the connecting piece are inserted together in a sliding fit mode, cables are connected to the tails of the connecting piece and the inner shell in a sealed mode, and the joint of the cable in the connecting piece and the cable in the inner shell is located in a closed space formed by the inserting piece and the inner shell; the connectingpiece and the inner shell are connected in an inserted mode to form three waterproof layers. According to the moistureproof connecting structure of the underground cable, the connecting piece and theinner shell form a plugging state under the cooperation of the outer shell and the plugging piece, and the inner thread on the outer shell and the outer thread on the inner shell are engaged with each other through the relative rotation between the inner shell and the outer shell so as to form a fixed connection state; the partition type internal threads and the partition type external threads facilitate insertion and connection actions and save thread meshing time, and fixed connection can be completed only by relatively rotating the half-circle connecting piece and the inner shell at most.