The invention relates to a seal structure of an underwater wet-type electrical universal connector. The seal structure comprises a seal cavity and a seal ring. The seal cavity is arranged in a connecting socket of the connector; a jack of the connecting socket is arranged in the seal cavity; the seal ring is arranged on a pin of a connecting plug of the connector and can move along the pin; the jack is internally provided with a piston; and when the connector is connected, the pin pushes the piston into the jack, and is connected with a conductive sleeve in the jack. Liquid cannot enter the electric connection position of the connector in the plugging process of the pin, thereby preventing damage to the connector due to short circuit and prolonging the service life of the connector.