A rotating shaft oil seal mainly solves technical problems that the sealing effect of the existing rotating shaft oil seal is relatively poor, etc. The technical proposal of the rotating shaft oil seal has the following points: an oil return hole is arranged in the centre of an outer sealing cover; a cylindrical chamber with the outer diameter larger than that of the oil return hole is formed in the centre of the inner side of the outer sealing cover; a clearance groove with the inner diameter than that of the cylindrical chamber is formed at the bottom part of the inner side of the cylindrical chamber of the outer sealing cover; inner screw saw-shaped teeth are arranged on the inner wall of the cylindrical chamber of the outer sealing cover; a rotating body is sleeved on and matched witha shaft in the cylindrical chamber of the outer sealing cover; outer screw saw-shaped rotating teeth are arranged on the periphery of the rotating body, and are correspondingly matched with the saw-shaped teeth of the outer sealing cover; both the outer sealing cover and the rotating body adopt a split type which is formed by fixedly connecting two or more parts; the fit between the saw-shaped teeth and the rotating teeth enables component force generated in high speed rotating process to cause a liquid to rebound to form eddy current so that the sealing effect is good; and the higher the rotating speed is, the better the sealing effect is. The bearing can be cooled to ensure the quality of bearing lubrication. The rotating shaft oil seal is mainly applied to the rotating shaft oil seal of a horizontal rotary mechanical bearing block adopting a medium to lubricate.