The invention discloses an automatic flaw detection line, which comprises: a front end feeding device, a magnetizing spray detection device and a rear end feeding device. During work of the detection line, horizontally arranged rollers are sent to a roller clamping mechanism through the front end feeding device, a conducting rod of the roller clamping mechanism clamps the middle roller and performs magnetizing, at the same time, a driving mechanism works to drive the rollers to rotate and spray fluorescent magnetic powder liquid, then the roller surfaces are photographed by a CCD camera on the detection mechanism, and a detection control system judges whether the roller is accord with the quality requirement according to fluorescent magnetic powder traces on the photographs. The automatic detection line provided by the invention has a simple structure and is convenient to use, can realize automatic operation of magnetizing, spraying of the fluorescent magnetic powder liquid and photographing. Therefore, the whole roller flaw detection realizes automatic operation, the production efficiency can be effectively improved, the labor cost is lowered, the detection quality is improved, and then the rail transit vehicle quality can be effectively guaranteed.