Numerical simulations were made for optimizing a micro-pump with step electrodes. A pair of step electrodes is placed repeatedly on the bottom wall of a micro-channel. An AC voltage is applied to each pair of step electrodes. Such a design is known for faster pumping than a pump with planar asymmetric electrodes does. The conventional approach based on linear assumptions is limited to low external voltage, at most 25㎷. Hence, the Steric effect were includes in simulations, which has the capability to predict flow behaviors at large voltages.' This study presents geometrical optimization of the pump. In addition, the effects of the magnitude and frequency of external voltage on pumping flow rate is scheduled to be studied in the future.