Abstract: Aiming at the problem of scratch depth detection in the process of locomotive axle maintenance, a portable white light confocal axle surface scratch detection device was designed based on the dynamic exposure compensation method of axle metal surface and scratch area compensation algorithm. Through the systematic and intensive design of the confocal sensor, portable displacement slide and control system, the on-site detection of axle surface scratch was realized. The experimental results show that the device can measure the metal reflective surface with an accuracy of ±1.8 μm. In the precision verification experiment with a standard single-scribed line template, the maximum indication error was −2.3 μm.