Abstract: Steel tube W. T.increment was measured during the operation of non-stretch reducing mill on the Φ100mm plug pipe-rolling line.The resultant data show that under normal operation conditions, it is logical to calculate the gauge increment with equation:△S=0.0044△D. Sc, and that in case of pipe-reducing with Sc<10mm and 15mm>Sc ≥ 10mm, proper correction should be made to the calculated W.T. increment.