Analysis of the concentration distribution in a gas centrifuge cascade for separation of multicomponent isotope mixtures is different from that in a cascade for separation of two-component mixtures. This paper presents the governing equations for a multicomponent isotope separation cascade. Numerically predicted separation factors for the gas centrifuge cascade agree well with the experimental data. A theoretical optimal feed position is derived for a short square cascade for a two-component mixture in a close-separation case. The optimal feed position for a gas centrifuge cascade for separation of multicomponent mixture is discussed.