There are some heavy metals in the electric arc furnace (EAF) steelmaking dust. It has been listed as a hazardous material because it is harmful to the environment to landfill the EAF dust. The valuable metals in the dust can be recycled by mixing it with reducing agent carbon to make pellets and then returning the pellets to the 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, which is not only to protect environment but also to recover metals in the way of the direct reduction. But the lignosulfonate was used as the binder in the pelletization and the sulfur in it maybe affects 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 removing in EAF dust reduction process were determined by thermodynamics calculation study on CaO MgO FeO Fe 2O 3 SiO 2 S slag at 1 550 ℃. The oxidation ability of slag can be expressed as n (FetO)= n (FeO)+6 n (Fe 2O 3)+8 n (Fe 3O 4). The relationship between the sulfur removing ability and the oxidizing ability, the ratio of ferro silicon, lime as well as the basicity of the slag was determined on the study. The calculation thermodynamics model was set up and it could be useful in production. [