Abstract: Relevant theoretic analysis and simulation calculations are conducted with considerations of such elements relating the weld pipe sizing process as rigidity of the sizing mill base, manufacture accuracy of the sizing equipment, and the sizing amount and passes, etc. As a result, how the elements like the sizing equipment and sizing process influence the O.D. tolerance of the stainless steel weld pipe is identified. Based on the analysis, it is concluded that the critical element for improving O.D. tolerance of the stainless steel weld pipe is to improve the manufacture accuracy of the sizing equipment, while such necessary measures as increasing sizing amount and sizing passes have to be imposed.