Abstract: In order to ensure the safety of railway transportation, unmanned aerial vehicle (UAV) visual detection technology on gauge-exceeding for railway freight car was put forward in this paper. Based on the model of the UAV flight attitude, taking multi angle UAV to photograph railway freight car loading image, the 3D model of railway freight car could be restored on the basis of the monocular stereo vision 3D measurement theory and image data processing methods. After nesting and comparing the reconstructed model with the gauge-exceeding standard model, the gauge-exceeding status of the whole railway freight car could be determined precisely, which avoided the security risks resulting from the manual measurement. The gauge-exceeding inspection experiment demonstrates that the detection precision is up to 2 mm.