The invention discloses a movable online detection device and a movable detection method of an enamelled wire diameter. As the detection device and the detection method are adopted, defects existing in the traditional detection method are overcome, the enamelled wire diameter in an on-line way can be directly and effectively detected, and the detection device and the detection method are simple in operation, convenient and effective, low in production cost, and improved in production efficiency. The invention is realized by the following technical: the movable online detection device comprises a laser diameter measuring instrument, an enamelled wire compacting device, a horizontal mechanism which can drive the laser diameter measuring instrument and the enamelled wire compacting device to move horizontally, a longitudinal mechanism which can drive the enamelled wire compacting device to move longitudinally, a driving device and a controller, wherein the enamelled wire compacting device is connected with the horizontal mechanism and the longitudinal mechanism, the laser diameter measuring instrument is fixed on the horizontal mechanism, the controller controls the horizontal mechanism and the longitudinal mechanism to act and controls the laser diameter measuring instrument to detect the actions, and the laser diameter measuring instrument sends detected data information to the controller for qualified judgment.