The thermal diffusion is one of the useful methods for the hydrogen isotope separation. The experiments using ‘Cryogenic—Wall’ thermal diffusion column cooled by liquid nitrogen have been performed in the total reflux and the withdraw modes. As using the same inner diameter column, ‘Cryogenic—Wall’ thermal diffusion column has the higher separation factor, but the lower optimum pressure than ‘Ordinary—Wall’ thermal diffusion column cooled by water. It is obtained that ‘Cryogenic—Wall’ column with a smaller inner diameter has the remarkable high separation factor and the higher optimum pressure. In the withdraw mode, the characteristics of the separation factor as a function of the feed rates is obtained about the several inner diameter columns.