Abstract: To counter its characteristics of far from equilibrium,the metallurgical reaction occurred at slag/metal interface for SiO₂ in molten slag with deposited metal had been modeled in view of coupling non-equilibrium static thermodynamics with interacting principle of liquid-liquid phases. According to the established model,nonlinear numerical simulation was carried out with matlab software.The result of quantitative calculating shows that there is obvious distinction in direction and limitation for different welding zones.The distance of drifting off equilibrium state for straight oxidizing direction in droplet stage is far more than that of inverse reducing direction in welding pool zone.Meanwhile,factors such as temperature,SiO₂ content exert certain influence on direction and limitation of chemical reaction,which produces great impact on oxygen gaining for weld metal.