A watertight joint and a plug-in device are provided. The watertight joint includes a gland, a plug, an end cap and a sleeve cover, wherein the end cap includes a cable, a wrapping body and a sealing ring, wherein the wrapping body is wrapped on the cable and in a cone-shaped structure, and the sealing ring is sleeved over the second end of the wrapping body, the plug is fixedly connected to the port of the cable, the sleeve cover and the gland are sleeved over the wrapping body, opposite to each other, and the sleeve cover and the gland are in threaded connection, and the inner wall of sleeve cover abuts on the sealing ring.