Abstract: The root cause that restrains yield of the Φ610 mm HFW pipe production line is identified by means of the Six Sigma Method containing such tools as Plato, Student's T test, non-parameter test, and variance analysis. Accordingly, corrective actions are determined and taken to optimize forming and welding processes, and modify inner burr cutter bar. As a result, the yield of the said production line has been increased by 14.2%, and the yield Sigma level has been also enhanced from the original 0.66 to 1.23.