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 (32-1) and a movable core (32-2) being controlled to move by turning on and off the traction coil (32-1), wherein the locking pin is fixedly connected to an end of the movable core (32-2) away from the traction coil (32-1), wherein the movable core (32-2) 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 (32-2) 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 (32-1) and a movable core (32-2) being controlled to move by turning on and off the traction coil (32-1), wherein the locking pin is fixedly connected to an end of the movable core (32-2) away from the traction coil (32-1), wherein the movable core (32-2) 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 (32-2) passes is disposed on an inner wall of the first barrel in a direction corresponding to the locking hole . <EOS>