Abstract: Analytical calculation of the rigidity of the 3-roll mandrel pipe mill is theoretically conducted with related knowledge concerning contact mechanics and material mechanics to deduce the calculation formulas for rigidities of different components of the mill.The rigidity of each individual component of a certain type mandrel mill is verified with relevant FEA software，and in this way the rigidity calculation formula for each component is verified，too.Based on the summary of the rigidity calculations，the overall rigidity of the mill is found out，and then the rigidity of the mill is tested on the site.The analysis result shows that the said analytical calculation formula for the component rigidity of the mill can bring about rather high accuracy；the overall rigidity as obtained via the on-the-site testing is close to the calculation result via the analytical formula，and the error is just within 5%.The results from the verifications with both the FEA software and the on-the-site testing method have proven the reliability of the above mentioned analytical formulas.