An effective passive micromixer based on the T-shaped channel with periodic baffles mounted on the bottom of main channel was designed to enhance the mixing performance of the microfluidic system. Instead of complex spacial geometries, simple periodic geometric features were used to decrease the required mixing distances and time and to obtain remarkable mixing efficiency. With an orthogonal array, the effects of geometrical parameters on the mixing performance were studied by numerical simulations using commercial computational fluid dynamics code ANSYS CFX. A static Taguchi analysis was taken to evaluate the relative effectiveness of the geometrical parameters. The analysis results indicate that the relative effectiveness can be ranked as: the angle of attack(θ)>microchannel height(H)>baffle width(L)>baffle spacing(D). Based on the relative effectiveness of the geometrical parameters, an optimal parameter group selected are θ=75°, H=0.4Wm, L=0.7Wm, D=0.6Wm(here Wm is the channel width with a value of 200 μm). It demonstrates that the mixing performance of the micromixer with optimal parameter group is improved obviously, and a complete mixing(mixing index M is better than 95%) can be obtained when the Reynolds number Re is 54. The characteristics of the pressure drop depending on the geometrical parameters are also investigated, and the result shows that the selected θ affects the pressure drop in a similar way under different Reynolds numbers, so does the selected H and D.