Abstract: The production line control system based on SIEMENS L2 network frequently jammed because of a large numbers of control nodes and heavily data exchanging, the system was improved by:1) reducing the nodes on the L2 network and shortening the length of network;2) dividing the L2 network into two networks which were physically independent but connected in terms of data communication.In the modified system, the amount of data on each network was reduced, the communication was speeded, and the network jam was eliminated.