An automatic control system is developed for a rolling shear line in this paper in order to overcome the weakness of the traditional control system. All of motion mechanisms are driven by alternating current motors. The S7-300 PLC is selected as the control unit. And the PROFIBUS-DP field bus is employed to structure a distributed control system. Automatic cutting to length is realized. The rolling shear line has some merits such as high efficiency and precision, low cost and energy consummation ensured by the control system. The control system is reliable and flexible.