Abstract: The consistency of the rolling centerline of each unit in the production of the hot-rolled seamless steel pipe is a prerequisite for ensuring the dimensional accuracy of the steel pipe. Using the laser tracker，the rolling angles and center lines of the piercing mill and mandrel mill proper of the Φ273 mm mandrel pipe mill plant are measured and calibrated with high accuracy so as to ensure that the centerline of each unit’s pass coincides with the rolling centerline. After checking the accuracy of the laser tracker with the OmniCal software，3D coordinate measurements are taken separately on the center points of each unit with the SpatialAnalyzer software，and then a coordinate system is established. By using the automatic tracking target ball equipped with the laser tracker to collect the required measurement points，the corresponding 3D graphics are fitted to obtain the deviation of the required data，based on which each unit of the mill plant is correspondingly adjusted，so as to get the pass center line of each unit of the mill plant coincided with the rolling center line.