Online monitoring system and online monitoring method for surface quality of metal piece

The invention provides an online monitoring system for the surface quality of a metal piece and a method using the system. The online monitoring system comprises a monitoring terminal provided with a defect comparison database. The front surface quality detector is arranged at a first station in a monitoring area where the metal piece passes through the online monitoring system, obtains surface defect information of the metal piece and sends the surface defect information to the monitoring terminal; and the rear surface quality detector is arranged at a second station where the metal piece enters the monitoring area of the on-line monitoring system, obtains image information of the defect position of the metal piece, and sends the image information to the monitoring terminal. The first station is arranged in front of the second station, and the monitoring terminal performs data analysis on the surface defect information of the metal piece from the front surface quality detector and the surface defect informat