A locking mechanism for a gauge-changing wheelset, wherein a plurality of locking holes are disposed on an inner hub of wheels of the gauge-changing wheelset at intervals in an axial direction; the locking mechanism comprising a locking pin and a traction electromagnet; wherein the traction electromagnet comprises a traction coil and a movable core being controlled to move by turning on and off the traction coil, wherein the locking pin is fixedly connected to an end of the movable core away from the traction coil, wherein the movable core is configured to drive the locking pin to insert into or remove from the locking hole to lock or unlock the wheels; and the locking mechanism further comprising a sleeve, wherein the sleeve comprises a first sleeve and a second sleeve connected with the first sleeve, the first sleeve comprises a first end cover and a first barrel, the first barrel extending toward the wheel side in a circumferential direction of the first end cover, and the first end cover is provided with an axial through hole and is tightly connectable with an axle of the gauge-changing wheelset through the axial through hole; the second sleeve comprises a second end cover integrally connected with the first barrel in the circumferential direction of the first barrel and a second barrel extending toward the wheel side in a circumferential direction of the second end cover; and, in a mounted position of the sleeve on the axle, the inner hub of the wheel extends into the first barrel and is slidably fitted with the first barrel, and a through hole through which the movable core passes is disposed on an inner wall of the first barrel in a direction corresponding to the locking hole. the locking mechanism comprising a locking pin and a traction electromagnet; wherein the traction electromagnet comprises a traction coil and a movable core being controlled to move by turning on and off the traction coil, wherein the locking pin is fixedly connected to an end of the movable core away from the traction coil, wherein the movable core is configured to drive the locking pin to insert into or remove from the locking hole to lock or unlock the wheels; and the locking mechanism further comprising a sleeve, wherein the sleeve comprises a first sleeve and a second sleeve connected with the first sleeve, the first sleeve comprises a first end cover and a first barrel, the first barrel extending toward the wheel side in a circumferential direction of the first end cover, and the first end cover is provided with an axial through hole and is tightly connectable with an axle of the gauge-changing wheelset through the axial through hole; the second sleeve comprises a second end cover integrally connected with the first barrel in the circumferential direction of the first barrel and a second barrel extending toward the wheel side in a circumferential direction of the second end cover; and, in a mounted position of the sleeve on the axle, the inner hub of the wheel extends into the first barrel and is slidably fitted with the first barrel, and a through hole through which the movable core passes is disposed on an inner wall of the first barrel in a direction corresponding to the locking hole.