Abstract: To meet the need for producing extra-long cold-drawn steel pipes with the 400 kN(40t) cold-drawing mill,the automatic control system thereof is modified with a control solution based on the Siemens S7-200 PLC. Elaborated in the paper are the composition,realization method and software programming of the said automatic control system. The system as modified is capable of full-auto control,interlock control and alarm for fault alarm,etc. of the cold-drawing mill. The actual application result of the system is very satisfactory.