Abstract: 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 1-5V 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.