Abstract: In order to avoid the railway traffic accidents caused by geological disasters, an effective railway geological disasters monitoring and early warning system should be established. Mountain crack gauge was a kind of automatic measurement equipment which was designed to monitor the changes of mountain cracks. The crack width of the mountain is one of the most effective criteria for the early warning of geological disasters. It was implemented automatic data acquisition, issued alarm signal when the change rate of the mountain crack exceeded the warning value. The mountain crack gauge was applied to railway geological disaster monitoring and early warning project in the southwest area, and a certain effect was achieved. The gauge could be used to track the development trend of disaster automatically, prevent and reduce the occurrence of major accidents in advance, ensure traffic safety, provide important key parameters and theoretical support for the geological disaster monitoring outside the railway system.