Aiming at the complexity of the traditional gauge detection method, high requirements for the installation and large amount of data analysis, a gauge measurement method based on the relative transverse movement of wheel and rail is designed in this paper. Two sets of laser source and camera combinations are used to dynamically collect the image of the inner straight line part of the rail head in the method. According to the rail parameters, the Hough detection and perspective transformation are used to rectify the image from the same acquisition distance. Compared to datum moment, the variation of vertical displacement of the center point of the laser is computed. And through the geometrical relation of the variation previously described and the lateral relative displacements of the two wheels, the relative transverse displacement of the two wheels is calculated. The relative initial time gauge change is gained by the difference, which realizes the indirect measurement of the track gauge. The experimental results show that the method has the characteristics of simple hardware structure, small data calculation, high measurement precision, and can realize non-contact dynamic measurement of gauge parameters.