The invention provides a half-ring sealing structure for sealing a shaft part. The half-ring sealing structure comprises an upper housing, a lower housing, a transition block, a special-shape sealing ring and an axial sealing ring, wherein the axial sealing ring enclasps a step shaft; the special-shape sealing ring is placed in a sealing groove of the upper housing or the lower housing; the transition block is arranged among the upper housing, the lower housing and the step shaft, and is used for smooth transition of a sealing structure part; and hexagonal bolts and hexagonal nuts compress the upper housing and the lower housing, and a sealing cavity is formed. With the adoption of the half-ring sealing structure, the sealing structure part can be formed on the step shaft, and the sealing is reliable. The half-ring sealing structure has the advantages of simple and novel structure, reliable sealing, high adaptability, and the like, can act as a special-shape step shaft to form the sealing cavity for conducting airtight detection, and can also be used for sealing of a rotating shaft in mechanical equipment, such as a gear box.