As a critical part of the train, wheels affect railway transport security to a large extent. This paper introduces an online method to detect the wheel tread of a train. The wheel tread images are collected by industrial linear array charge coupled device (CCD) cameras when the train is moving at a low velocity. This study defines the positioning of the cameras and determines how to select other parameters such as the horizontal angle and the scanning range. The deformation of the wheel tread image can be calculated based on these parameters and corrected by gray interpolation.