It　is　the　key　problem　to　realize　stable　arc　welding　process　with　high　current　and　low　voltage　in　order　to　avoid　the　undercut　occured　in　high　speed　arc　welding.　A　new　kind　of　single　cycle　voltage　feed　back　control　system　was　designed,　which　ensured　the　constant　average　voltage　and　stable　arc　length　in　each　pulse　cycle.　Noise　voltage　was　cut　off　and　waveform　of　current　during　short　circuit　was　controlled.　It　is　demonstrated　that　the　system　has　an　excellent　arc　length　self-adjusting　ability.　Compared　with　conventional　welding　power　source,　the　working　voltage　of　the　system　can　be　decrease　about　1-5　V　at　the　same　wire　feed　rate.　The　welding　bead　is　very　nice　and　defects　are　completely　avoided　when　the　welding　speed　is　high　as　1.3　m/min.