The utility model relates to the field of rail vehicle gauge changing. The axle for the gauge-changeable wheel set comprises an axle body, non-circular wheel seats are arranged at the two ends of theaxle body respectively, the cross sections of the non-circular wheel seats are similar to polygons, the non-circular wheel seats are used for installing wheels, and the shape of axial through holes ofthe wheels is matched with the shape of the non-circular wheel seats. The variable gauge wheel set can achieve the purposes of transmitting torque, releasing the axial freedom degree and having goodbearing capacity, the structural function of the variable gauge wheel set is achieved, and meanwhile the reliability of the variable gauge wheel set is improved.