Abstract: In order to achieve the railway locomotive gauge measurement with high efficiency and high precision,a scanning laser-based gauge detector was designed.The cross-section scanning measurement was realized by fixing ranging sensors around the support frame.The field high-precision calibration method was focused.The system parameter was calibrated with the self-designed calibration card and the laser tracker.The system parameters,combined with the ranging sensor measurements,were used to calculate the 3-D coordinates of all the measured points in the rail coordinate system,and then the distance between the cross-sectional profile and the standard gauge was calculated so that the clearance was measured.Field experiments show that the system is in high efficiency and the system measurement accuracy of 0.5mm meets the need of bound detection.