Abstract: A PLC-based external welding slag removing-collecting system for large-sized SAW straight welded pipe production line is developed by Hebei Huayou Steel Tube Design & Research Institute.Described in the paper are the configuration and operating principle of the system,and design of the software and hardware for the PLC-based electrical control system.Also discussed are the reliability,anti-interference and maintenance of the said welding slag removing-collecting system.