The low pressure mercury lamp has been used as the sterilization technique by UV light. However, short time high efficiency sterilization have been required in recent years. Although the plasma arc is one of the highly intense radiation medium, there is few papers of sterilization by a plasma arc. The number density and net emission coefficient of high temperature argon mixed with iron or mercury vapors are calculated by using a line spectrum emission, free-bound emission, and free-free emission equations. The high net emission coefficient of UV ray emitted from argon-iron gas is obtained. Fe II from argon-iron gas is dominant in UV ray wavelength range. The tendency of the spectrum characteristic of sterilization about the wavelength of argon-iron gas obtained. Especially, a strong emission was obtained at 259nm for argon-iron gas. The net emission coefficient of argon-iron gas is larger than that of argon-mercury gas from 200 to 300nm. Mercury vapor has few spectrum lines and the net emission coefficient becomes small. Therefore, the argon-iron gas is applicable to UV ray sterilization.