The invention discloses a multi-stage part concentric assembling device and method. The multi-stage part concentric assembling device comprises a cross supporting frame, positioning blocks and slidingguide structures, wherein two of the positioning blocks are fixed on each of four supports of the cross supporting frame; one sliding guide structure is arranged between the two positioning blocks oneach support; a sliding stop block is arranged on each sliding guide structure; and a threaded hole is formed in each positioning block. After a first workpiece and a second workpiece on inner and outer rings are fixed, the sliding stop blocks can move up and down flexibly, and when blades are assembled, a third workpiece and a fourth workpiece can flexibly move, so that the normal assembly of parts on the positioning blocks is not affected, and the assembly efficiency is improved; after the blades is assembled in place, the fourth workpiece is constrained to a set position by the sliding stop block, and therefore the concentricity requirement is directly kept within 0.2 mm; and the assembling process is not affected by deformation of the fourth workpiece with thin wall so as to influencethe assembling precision, and meanwhile, the fourth workpiece can be corrected by adjusting the positions of the sliding stop blocks.