The invention discloses an oil leakage preventing, fastening and sealing device for an outgoing line and a method for applying the oil leakage preventing, fastening and sealing device. The oil leakage preventing, fastening and sealing device comprises a compression sealing gasket, a fastening and sealing device shell and a compression nut. The fastening and sealing device shell comprises a screw tube and a nut, threads A are arranged on the outer surface of the screw tube, the compression sealing gasket sleeves the screw tube and is arranged at the left end of the nut, a sealing plug is arranged in the screw tube, at least two outgoing line holes are formed in the sealing plug, a sealing plug locking device is arranged at the right end of the sealing plug, a left body of the sealing plug locking device extends into a space between a right body of the sealing plug and the screw tube and is clamped in the space between the right body of the sealing plug and the screw tube, a large-diameter right body of the sealing plug locking device is in contact with the screw tube, threads B are arranged on the inner surface of the compression nut, and the compression nut is arranged at the right end of the sealing plug locking device, compresses the sealing plug locking device and is fixed to the screw tube in a threaded manner. The oil leakage preventing, fastening and sealing device and the method generally have the advantages of reasonable structure, good oil leakage preventing, fastening and sealing effects and high field adaptability.