The invention relates to the technical field of shaft connection, and provides a connecting structure. The connecting structure is used for connecting a connected part to a thin-wall transmission shaft, and the connected part is provided with an inner ring surface; and the connecting structure comprises at least one first clamping groove, at least one connecting key and a lock ring, wherein the first clamping grooves are formed in one end, connected with the connected part, of the thin-wall transmission shaft, the connecting keys are arranged on the inner ring surface of the connected part, the lock ring is provided with an outer ring surface, at least one connecting groove cooperating with the connecting keys is formed in the outer ring surface of the lock ring, the lock ring is providedwith a first end surface and a second end surface which are oppositely arranged, and clamping strips capable of being inserted into the first clamping grooves are arranged on the first end surface. Byusing the connecting structure, external splines are prevented from being arranged on the thin-wall transmission shaft so that the wall thickness of the thin-wall transmission shaft can be set in a relatively small mode.