The automatic production line in mechanical machining has the features of a large number of interactive signals, complicated logical handing and large amounts of distribution lines. In order to solve these problems, Mitsubishi Q-series programable logical controller (PLC) and control & communication link (CC-Link) field bus are used to realize the signals and data communication including robots, computer numbercial control (CNC) machines, forehearth and other devices. According to CC-Link network diagram, the setting of CC-Link network parameters was introduced in detail. The PLC control program to realize signals communication was given by taking an example. The monitoring system of automatic production line was developed by MELSOFT GT Designer3, which could monitor the running status of equipment and diagnose the CC-Link network communication. The control, alarm and diagnosis of machining of automatic production line of a certain part in automobile industry are realized finally.