The present disclosure provides a method and system for detecting a gauge of a metro vehicle. The method includes obtaining a plurality of partial three-dimensional contour images and a first identification information of the vehicle during a course of the vehicle passing through a transition track; processing the plurality of partial three-dimensional contour images of the vehicle to get a complete three-dimensional contour image of the vehicle; determining a gauge judgment result of the vehicle according to the first identification information, a preset gauge standard image library and a complete three-dimensional contour image of the vehicle; and sending the gauge judgment result of the vehicle to an Automatic Train Supervision (ATS) module. With the method and system for detecting the gauge of the metro vehicle, the efficiency of the vehicle gauge detection is improved and the automatic vehicle gauge detection is achieved.