Determining the concentration distribution of mixture components in a separation cascade plays an important role in analyzing and optimizing separation performance. A new iterative method, called the "q-iteration method," is presented to solve the nonlinear difference equations describing the concentration distribution of a multicomponent mixture in separation cascades at steady state. Iteration takes place over quantity q, the ratio of the head concentration to tail concentration of certain components, other than the concentration itself in commonly used methods. Numerical tests are carried out for both short and long square cascades. Comparisons are made with the transient approach. The results show that the new method is both robust and efficient.