Abstract: In order to analyze the stress situation of the molten pool in horizontal pulsed SAW (submerged arc welding), the pool was simplified into a piece of liquid metal on the surface of solid metal, which receives pulse load regularly.In this way, the mechanism of undercut elimination with pulse current was brought forward, i.e.the arc force loaded to the pool, the impact force of droplet transfer and the resultant surface tension all follow the regular pulse current change.Such regular change of these forces helps to eliminate the undercut.The forces follow the regular changes of pulse current, and the peak value of certain pulse current ensures a pleasant penetration to prevent incomplete penetration.The pulse current can also restrain the undercut.Therefore, the range of processing parameters in ordinary horizontal SAW can be increased with the technology of pulse horizontal SAW.