Abstract: Discussed are certain calculation issues related to the straightening screwdown rate in the six-roll cross-rolling seamless steel pipe straightening mill. The straightening process is deeply analyzed using the elasticplastic straightening theory and then a calculation methodology is developed for the practical straightening screwdown rate in the above mentioned straightening mill and the calculation results for several kinds of pipes are compared. Testing results show the actual screwdown rate should be the sum of that of theoretical rectification and that of straightening. The results offer an optimal method of selecting straightening screwdown rate and provide a theoretical basis for improving the straightening precision and developing the best straightening process.