Abstract: In this paper, weld seam tracking method based on micro-beam plasma arc is developed. A non-transferred plasma arc was setup by a micro-beam plasma generator, then the plasma flame resistance between the nozzle and the workpiece was measured. Results show that, there is a clear relationship between the resistance and the torch height. If a scan set is equipped, the weld seam position can be detected. Fundamental experiments were done to show the influences on the resistance by sustained arc current, nozzle structure, electrode diameter, and plasma gas flow etc.