Abstract: The three-roll plug steadier is one of the key units of the seamless steel tube operation line.The work theory of the pipe mill plug steadier is described.With the analytic method, a new three-roll plug steadier which ensures the synchronous movement of the three sets of 4-linkage mechanisms is successfully designed.Thanks to the said design, the new type three-roll plug steadier has such advantages as being easy for assembling/disassembling and maintenance, simplified structure, compact outline and easy control of opening so as to enhance the consistent rolling operation and improve the dimensional accuracy of the tube.