Abstract: In this paper,CO₂ arc welding transition is studied deeply and the parameters are analysed quantitatively.The mathematical models of wleding source and arc length are simplified and the relative function of inductance and arc is determined by welding wire diameter and feed in velocity.The relation of inductance and short circuit current is approached to the mathcmatical model of multizone function.A practical mathematical model is deduccd by numerical value imitation,the suitable simplification is done,and boundary condition is defined.The model is translated computer software by computer high language.The change of output waveform can be observed by simulated oscillograph.The results of emulation and practice are very close.