The invention discloses a train fault detecting method and system. The method comprises the steps that an image of a train on which fault detecting needs to be carried out is obtained; whether a standard template image corresponding to the image exists in a database is judged; when the standard template image corresponding to the image exists in the database, a first preset algorithm is adopted for comparing the image with the standard template image and obtaining a comparison result; whether difference exists between the images is judged according to the comparison result; if yes, the position of the difference between the images is labeled to determine that faults exist in the train. It can be seen that comparison analysis of the image is used for replacing on-site detection in the prior art, namely, a large number of technical staff do not need to go to sites for detection, and a lot of manpower and material resources are saved; moreover, the comparison analysis mode can be realized automatically through electronic equipment, excessive manual participation is avoided, and the detection process is simple, efficient and objective.