The properties of ultra purity ferritic stainless steels and the difficulty of carbon and nitrogen removal from its molten steel were expounded. Based on the thermodynamic theory and the research results , the influence factors of decarburization and denitrogenization in VOD were discussed, and the smelting data in spot was statistically analyzed. Lastly, the modified process measures, such as controlling high vacuum, strongly blowing argon from bottom, increasing the temperature of the liquid steel into VOD, raising carbon content and decreasing nitrogen content of molten steel into VOD, strengthening blow��oxygen volume during decarburization, completely blowing argon process in high vacuum and choosing low carbon or no carbon material and so on, were presented for smelting ultra purity stainless steels in VOD and the development after adopting the technology was introduced in TISCO.