Abstract: In order to decrease fluctuating of pulse frequency and welding current while adjusting arc length, the frequency-character combine controller of arc length adjustment was researched and designed in GMAW-P welding machine based on digital signal process controlling.Base time and welding voltage setting were used as controlling variables in order to ensure pulse frequency within small change during arc length adjustment.The experiments show that this control method of arc length adjustment has the characteristics of fast adjusting and good stability;welding current, pulse frequency can change smaller when arc length is disturbed.