Abstract: The expressions of separative power of both binary isotopic and multi-isotopic mixture are presented. The isotope separation experiments are performed on a single separating unit, using SiHCl3 (Silicochloroform) as the working gas. The relations between feed flow and each parameter which characterizes the separative performance are obtained. The results show that the separative performance of single unit reaches its maximum when feed flow is about 20 grams per hour.