The invention discloses a machining method and a machining device of a cobalt-base superalloy thin-walled sleeve part, and belongs to the technical field of machining. The machining device provided bythe invention comprises a clamp assembly and a mandrel. A workpiece is supported through the clamp assembly and the mandrel, the internal cylindrical surface and the external cylindrical surface of apipeline billet are machined, in the machining process, the pipeline billet is not prone to deformation, the machined workpiece inner and outer diameter wall thickness difference is small, the shapeprecision is high, and the workpiece surface roughness is high.