Abstract: Described here in the paper are the control system and the function for preventing retainer rack runaway accident of the MPM as located at a certain domestic company.Also detailed is how the said function acts to prevent runaway accident of the MPM retainer rack.Analyzed is the realization process of the program of the said function.It is identified via the analysis that the actual application of the said protection function to the Φ180 mm retaining mandrel pipe mill proves that the possible runaway accident of the retainer rack as always caused by miscarrying by the No.1 rolling mill is obviously avoided so as to get the operation efficiency of the retaining mandrel mill enhanced.