The invention relates to a sealed universal shaft which is suitable for the field of drilling oil and natural gas, is matched with a screw drill and comprises a middle shaft with an inner spherical hinge and an outer spherical hinge arranged at both ends. The sealed universal shaft is characterized in that a sphere at the top end of the inner spherical hinge is matched with an axial hall seat in an outer spherical hinge hole cavity by a supporting ball; a sealing device is arranged between the outer end of the outer spherical hinge hole cavity and the middle shaft and comprises a spherical end cover mounted at the outer end of the outer spherical hinge hole cavity; a sealing ring which is arranged by the end surface of the spherical end cover is matched with a sealing cover mounted on themiddle shaft; and the sphere of the spherical end cover is concentric with the spheres of the inner spherical hinge and the outer spherical hinge. The invention has the advantages that: (1) the innerspherical hinge and the outer spherical hinge have simple and compact structure and reliable working performance and are easy to process; (2) a sealing surface is more reasonably arranged so as to improve the sealing performance and prolong the service life of the universal shaft; and (3) a pressure-balancing device is arranged to balance pressure inside and outside the sealing cavity and have better sealing performance.