This article presents the effects of the desorbent flowrate (or m1) on simulated moving bed (SMB) process performance at constant m2, m3 and m4, where the m-values (mj) are defined as the net flowrate ratios of the zone, j, to the solid flowrate. A complete m-plane analysis of SMB systems (ComPASS) has been developed that illustrates how the desorbent flowrate is determined within the complete m-plane (i.e., fluid-solid flowrate ratio plane) to enhance the SMB process performance. The effects of desorbent flowrate are presented numerically for linear/equilibrium and nonlinear/nonequilibrium SMB processes. The results of the studies using ComPASS show that for linear/equilibrium SMB process, it is desirable to determine the minimum desorbent flowrate (m1) within the complete separation region. For the nonlinear/nonequilibrium SMB process, the desorbent flowrate can be determined at the minimum value which maximizes the raffinate purity.