A lubricating structure for gauge-changing wheelset, said lubricating structure comprising wheels, an axle, and sliding mechanisms; whereby - the wheels are slidably provided at both ends of the axle, and the sliding mechanisms are respectively connected to outer sides of the wheels and are located in axle-box bodies at both ends of the axle; - and the wheels are unlocked and locked by the sliding mechanisms; - a sealing structure is provided between an inner side of the wheel and the axle, a first cavity is formed between the inner side of the wheel, the axle and the sealing structure, a second cavity is formed between the outer side of the wheel and the sliding mechanism, and a third cavity is formed between the sliding mechanism and the axle-box body; - the sliding mechanism comprises an inner sleeve, the inner sleeve is in clearance fit with the axle, and one end of the inner sleeve facing the wheel extends beyond the axle-box body and is firmly connected with the wheel; - a gauge change space is reserved between the extending end of the inner sleeve and the axle, and the gauge change space forms the second cavity; - the sliding mechanism further comprises a rolling bearing and an outer sleeve; the inner sleeve, the rolling bearing and the outer sleeve are tightly sleeved in sequence from inside to outside, and the outer sleeve is in clearance fit with an inner surface of the axle-box body; - and the third cavity is formed between an outer end surface of the outer sleeve and an outer end cover of the axle-box body; characterized in that - the wheel is provided with first oil injection holes leading to a connection between the wheel and the axle, and the axle-box body is provided with second oil injection holes leading to the sliding mechanism; - opposite sides outside the outer sleeve are respectively provided with bosses axially extending along the outer sleeve, and a plurality of flutes are disposed at intervals along the length direction of the bosses; - an inner wall of the axle-box body is provided with concave arc surfaces corresponding to the flutes in a one-to-one manner; - locking pins are provided in locking spaces defined by the flutes and the concave arc surfaces in the axle-box body, and the axle-box body is also provided with third oil injection holes communicating with the concave arc surfaces. - the wheels are slidably provided at both ends of the axle, and the sliding mechanisms are respectively connected to outer sides of the wheels and are located in axle-box bodies at both ends of the axle; - and the wheels are unlocked and locked by the sliding mechanisms; - a sealing structure is provided between an inner side of the wheel and the axle, a first cavity is formed between the inner side of the wheel, the axle and the sealing structure, a second cavity is formed between the outer side of the wheel and the sliding mechanism, and a third cavity is formed between the sliding mechanism and the axle-box body; - the sliding mechanism comprises an inner sleeve, the inner sleeve is in clearance fit with the axle, and one end of the inner sleeve facing the wheel extends beyond the axle-box body and is firmly connected with the wheel; - a gauge change space is reserved between the extending end of the inner sleeve and the axle, and the gauge change space forms the second cavity; - the sliding mechanism further comprises a rolling bearing and an outer sleeve; the inner sleeve, the rolling bearing and the outer sleeve are tightly sleeved in sequence from inside to outside, and the outer sleeve is in clearance fit with an inner surface of the axle-box body; - and the third cavity is formed between an outer end surface of the outer sleeve and an outer end cover of the axle-box body; - the wheel is provided with first oil injection holes leading to a connection between the wheel and the axle, and the axle-box body is provided with second oil injection holes leading to the sliding mechanism; - opposite sides outside the outer sleeve are respectively provided with bosses axially extending along the outer sleeve, and a plurality of flutes are disposed at intervals along the length direction of the bosses; - an inner wall of the axle-box body is provided with concave arc surfaces corresponding to the flutes in a one-to-one manner; - locking pins are provided in locking spaces defined by the flutes and the concave arc surfaces in the axle-box body, and the axle-box body is also provided with third oil injection holes communicating with the concave arc surfaces.