Abstract: Elaborated in the essay are the modification of the billet hot-centering unit of the piercing mill in the hot-rolled seamless steel pipe production line by Jiangxi Hongdu Steel Works Co.,Ltd.,and the post-modification operation situation of the mill.The hot-centering unit features major functions,namely,guiding the billet into the tapered mould,setting the billet center as per the mould,and centering the billet in he mould via the punch pin.The operation practice shows that the centering accuracy of the modified device is much higher than that of any other centering device which features operating with the billet end face in a free-of-control state.