By a mathematical model of distribution behaviors of Ni, Co, Sn, Pb, Zn, As, Sb, Bi, Au and Ag in copper smelting process, accessory-element behavior was studied for two types of slag, fayalite and ferrite, and two levels of oxidation. The model can predict any set of controllable process parameters, such as feed composition, smelting temperature, degree of oxygen enrichment and volume of oxygen enriched air, in copper flash smelting, Mitsubishi and Noranda processes. The predictions by the present computer model were compared with the known commercial data from Guixi Smelter in China, Horne Smelter in Canada and Naoshima Smelter in Japan. The agreement between the computer predictions and the commercial data was excellent, therefore the present computer model can be used to monitor and optimize the actual industrial operations of copper smelting. The effects of oxygen enrichment, matte grade, smelting temperature and types of slag, on accessory-element behavior were elucidated.