The effects of geometric parameters on the mixing performance of a staggered herringbone mixer (SHM) with patterned grooves are numerically investigated. Combining use of the software package CFD-ACE+ and the Taguchi method provides a powerful and systematic approach for research on microfluidics. An orthogonal array L9(3(4)) is established for parameters introduced by the groove geometry; in total 9 cases are simulated. Analyses of the mixing phenomena, geometric parameter, pressure loss and flow rate through grooves are conducted. The modes of fluid motion and dominant mechanisms of mixing within the SHM are observed and ascertained. Although the depth ratio and the asymmetry index of the groove are found to be dominant geometric parameters, the rate of flow within the groove is verified to be the most significant factor that affects the mixing performance of a SHM. To date, the effects of the parameters are evaluated within specified ranges, and the true optimum design has yet to be discovered.