The invention discloses a sealing device, a centrifugal compressor and a gas turbine. The sealing device comprises an impeller hub, a diffuser body and a sealing part, the sealing part is located between the impeller hub and the diffuser body, the sealing part is arranged on the impeller hub, and the sealing part is located in front of sealing comb teeth in the leakage flow direction of a workingmedium, wherein the sealing part can rotate along with rotation of the impeller hub, so that the kinetic energy of the working medium flowing through the sealing part is reduced. According to the sealing device, when the sealing part rotates along with rotation of the impeller hub, the sealing part does positive work on the working medium in the circumferential direction and the centripetal direction of the impeller hub, and kinetic energy of the working medium flowing through the sealing part is reduced, so that the total pressure between the impeller hub and the diffuser body is greatly reduced, the pressure difference between the front portion and the rear portion of the sealing comb teeth is greatly reduced, the sealing effect is improved, the efficiency loss of the centrifugal compressor is reduced, and the efficiency of the centrifugal compressor is improved.