The invention discloses an on-line dynamic detection method and detector for a carbon fiber wire. The detector comprises a main rack, a driving mechanism, a detection mechanism, a mark mechanism and amaster controller, wherein the driving mechanism comprises rollers, a motor and a connection piece, the rollers are arranged at intervals, the motor is used for driving the rollers to rotate, the connection piece is used for connecting the driving mechanism and the main rack, the detection mechanism comprises an ultrasonic fault detector and a probe, the mark mechanism comprises a pigment bin, aspraying pump and a nozzle, the spraying pump is connected with the pigment bin, and the master controller is in electrical signal connection with each electrical control part. The whole detector is suspended on the wire and moves along the wire by the driving mechanism, automatic detection is achieved, manual intervention is not needed, and the detector is suitably used for overhead wire operation; the ultrasonic fault detector is used for performing non-destructive detection, and the detection efficiency is high; and due to the arrangement of the mark mechanism, a subsequent maintainer is convenient to timely find out a damage position of the wire, the special damage condition can be judged according to colors due to different mark colors, and the subsequent maintenance efficiency is improved.