Abstract: The relationship between the amount of the solid particles in arc atmosphere and the coat composite was analyzed by using welding fume drawing method. The results show that both the vaporized amount of NsF in gas phase,the product of metallurgical reaction in molten slag,and that of SiO₂ MnO in coat joining less metallurgical reaction are closely related to the coat composite content. Meanwhile a numerical model was built through non-linear and linear regression. The amount of NaF is proportional to the n power of fluorite content,and the constant coefficient is proportionally decreased with increase of the marble content, and that of SiO₂ MnO is proportionally increased with increase of the marble content.