The embodiment of the utility model provides an on-line diagnosis system for an electric locomotive, and the system comprises at least two data collection devices which are respectively disposed at anA section and a B section of the locomotive, and are used for respectively collecting the operation data of the A section and the B section of the locomotive in real time; and the at least two diagnosis devices are respectively connected with the corresponding data acquisition devices arranged at the locomotive A section and the locomotive B section, and are used for analyzing and diagnosing thelocomotive operation data acquired by the data acquisition devices in real time and displaying corresponding diagnosis results on display screens of the diagnosis devices. By means of the technical scheme, the problem that an original locomotive diagnosis system does not have a diagnosis function is solved, meanwhile, the whole locomotive diagnosis result of the corresponding locomotive is observed in any one of the A section and the B section, and the problem that locomotive workers cannot correctly find and handle locomotive faults is avoided.