When transferred type arc plasma is used for waste treatment and metal melting, the arc voltage may be changed by contamination of fumes and vapors from the molten bath. If the arc voltage goes over the open circuit voltage of the power supply, the arc extinguishes. On the other hand, if the arc voltage goes down, heat power and process efficiency decrease. This paper describes that the effect of contamination of iron vapor and fine particles on stabilized argon arc plasma. The calculations using transport properties and the energy equilibrium equation show decrease of axial electric field of arc column by contamination of iron vapor. This effect is maximum at the mixing rate of 3 to 5%. The tendency is almost same at the pressure range of 1 to 5atm. The experimental results on the wall stabilized arc contaminated by fine iron powders show good agreement with the tendency of calculations.