The invention relates to a dynamic bearing, which is characterized in that: a plurality of dynamic pressure grooves are arranged on the inner periphery of the dynamic bearing, and each dynamic pressure groove comprises two fork flow passages; wherein, the helix angle of the fork flow passage relatively inside the dynamic pressure groove is larger than that of the fork flow passage relatively outside dynamic pressure groove. The invention also relates to a rotating shaft; wherein, a plurality of dynamic pressure grooves are formed on the outer periphery of the rotating shaft, and each dynamic pressure groove also comprises two fork flow passages; the helix angle of the fork flow passage relatively outside the dynamic pressure groove is larger than that of the fork flow passage relatively inside the dynamic pressure groove. Meanwhile, the invention also provides a preparation method for the dynamic bearing. By designing the helix angle of the fork flow passage at one side of the dynamic pressure groove to be larger than that of the fork flow passage at the other side of the dynamic pressure groove on the dynamic bearing or the rotating shaft, the lubricating fluid can be kept in a certain region under the action of the pressure difference, thus effectively solving the problem of lubricating fluid leakage; meanwhile, by integrally forming the dynamic bearing and dynamic pressure grooves by means of fillers and a jet molding process, the quantity production and the stability of the products can be easily improved.