Abstract: In electron-beam(EB) scan welding, the 2D seam tracking could be approximated by combination of limited line segments and basic arc graphics, hence the whole welding processes could be divided into 3 steps: tracing of teaching, calculating of tracking data, and scan welding. In these processes, three main problems, non-vertical of x-y scanning axis, distortion of scanning track and defocusing of EB spot could be solved by proper conversion of oblique and rectangular coordinates, dynamic correction of deflection scanning magnetizing current with EB's deflection amplitude and velocity, and dynamic correction of focusing magnetizing current with EB's deflection vector, respectively. The welding results with "track field" type seam tracking reveal that, eccentric distance is above 0.08 mm, depth error is lower than 0.13 mm, width error in surface is lower than0.16 mm. The proposed welding method could precisely repeat the seam tracking and obtain excellent welding quality.