Abstract: Analyzed in the paper are the causes for the occurrence of the shell inner fold defect during the rotary piercing process for manufacturing the Ф107.95 mm×15 mm J55 seamless steel tube. Tests are conducted with different rolling data sets as selected and composed of screwdown amount,plug diameter,plug bar position,and distance between the guide shoes,etc. Based on the test results,relevant actions are taken,including reduching the screwdown amount,getting the plug bar position closer than before,increasing the plug diameter and cutting down distance between the guide shoes. As a result,an optimum data set consisting pre-piercing screwdown rate,compression frequency and the groove ovality factor is obtained,which has resulted in elimination of the pierced shell inner defect of the said J55 tube.