The utility model relates to an online automatic detection device for the abrasion of a pantograph pan of a locomotive. A front trigger switch and a rear trigger switch that are connected with data processing and control equipment are fixed at the position which is as high as the pantograph pan of the locomotive at the side surface of a detection shed; the left side and the right side of the detection shed are respectively provided with a left background plate and a right background plate; four image sensors are arranged on the detection shed; the visual angles of the left rear image sensor and the right rear image sensor are forward and downward and are respectively aligned with the front parts of the right background plate and the left background plate; when the rear trigger switch is triggered, the visual angles of the left front image sensor and the right front image sensor are backward and downward and are respectively aligned with the rear parts of the right background plate and the left background plate; and when the front trigger is triggered, the visual angles of the left front image sensor and the right front image sensor are respectively aligned with the right half part and the left half part of the pantograph pan of the locomotive. The online automatic detection device can be used for the online non-contact dynamic automatic detection for the locomotive and has high detection accuracy, good safety and convenience, good stability and reliability and long service life.