Abstract: Analyzed here in the article are the processing characteristics and difficulties of grinding process for external weld of the LSAW pipe. Addressing the problems concerning the helicity and non-straightness of the external weld of the pipe，an external weld grinding robot system is designed，and built up. The said system is equipped with the 6-axis industrial robot as the carrier of the grinding tool. The laser contour scanner is used to detect the weld height and track the grinding path. Described here are the main aspects of the robot system for flexible grinding of weld，including the overall design，the principle and the configuration of the lazar vision tracking system，and the process flow and the effectiveness of the grinding system. The result shows that the robot grinding system properly adapts the helicity and non-straightness of the straight weld，and is capable of automatically grinding the over-length external weld of the pipe body.