The invention provides a floating structure of combined herringbone gear inner gear rings. A planet gear is meshed with the inner gear ring A and the inner gear ring B, the inner gear rings and a floating gear ring are connected through a gear coupling, the floating gear and a connecting cylinder are connected through a gear coupling, a positioning plate is fixedly connected with the floating gear ring, a gap exists between the end face at the right side of the inner diameter of the positioning plate and the end face of the connecting cylinder in the assembling process, the two inner gear rings are axially positioned through a flange face at the right end of the connecting cylinder and a flange face at the left end of the floating gear ring and connected with the floating gear ring through the gear coupling, and gears are bevel gears symmetrically arranged. As the steering and rotation direction of the two semi simple bevel gear rings are reasonably matched, meshing axial force is offset, and the structural size is reduced; the flange faces of the structure parts are used for axial positioning, and compared with the mode of positioning through a clamping groove and a retainer ring, the strength of the thin-wall gear rings is effectively prevented from being weakened; the inner gear rings are not provided with fixed radial supports, the two-layer couplings are allowed to shift in the radial or angular direction and have good uniform load performance; the structure is more compact, and the assembling and disassembling manufacturability is good.