Abstract: The method of fitting and interpolation for the complex space curved welding seam tracking,depending on off-line samples teaching style by B3-spline curves,was introduced in this paper.In order to improve both accuracy and efficiency of interpolation in seam tracking,the improved dichotomy was proposed for changeable step-size control by the look-up table method.From the Matlab simulation results of pipe welding intersecting lines samples teaching,the methods above could be proved effectively in the process of weld seam tracking control,it provided experimental foundation for developing actual welding control system.Finally,the validity of the method has been verified by welding test.