The valuable metals in the dust can be recycled by mixing it with reducing agent carbon and lignosulfonate as the binder to make pellets, then reting the pellets to electric arc face (EAF) and adding ferro-silicon. Part of valuable metals in the dust is reduced by carbon and part of them reduced by ferro-silicon for the economical consideration. The reduced metals get into the steel in the stainless steel or special steel production. But the sulfur in the lignosulfonate may affect the quality of produced steel, which is dependent on the status of the smelting slag. The experiments were conducted in the way of changing the ratio of start iron, pellets, ferro-silicon and lime. The content of the slag was checked by XRF for the calculation thermodynamics study. The active concentrations of materials in the slag, the slag abilities of oxidation and sulfur removal in EAF dust reduction process were determined by thermodynamics calculation study on CaO-MgO-FeO-Fe2O3-SiO2-S slag at 1 550 ℃. The oxidation ability of slag can be expressed as N(FetO)=N(FeO)+6N(Fe2O3)+8N(Fe3O4). The sulfur removal ability is dependent on the amount of added ferro-silicon and the basicity of the slag. The calculation thermodynamics model was set up and it could be applied to the practical production.