Abstract: In the process of rotary piercing process of the seamless steel pipe，both the roll surface geometry and the rolling process parameters remarkably affect the groove opening.，particularly in the last service period of the piercing roll， due to the serious wear thereof，the error of the groove opening as calculated with the design parameters is rather large. The actual wear depth of the piercing roll is measured，and the calculation formula for the roll surface wear amount is described. Furthermore a high-precision calculation method for piercer groove opening is elaborated，involving consideration of such factors as the toe angle，the feeding angle and the uneven wear of the roll surface. And the application program is developed with the open source platform Lazarus，while a 3-D model with the roll surface wear characteristics is set up with SolidWorks. The software calculation result is compared with the SolidWorks measured result，showing that the calculation precision of above mentioned method is higher，and can meet the requirement for on-the-site real time application.