Two-dimensional micro mix driven by electroosmotic flow was studied by finite element simulation and mixes speed of microchannels with unified zeta potential of the wall surface and the polar opposite one was contrasted. Relation between the section shape of the microchannels and the speed of mixing is cleared when the wall surface has the polar opposite zeta potential. The results show that section mixing speed of microchannel whose wall surface with unified zeta potential is lower than the one with polar opposite wall surface zeta potential. The ratio of width to height in microchannels of homolographic rectangle section and the height of microchannels with isosceles trapezoid section also have influence on mixing speed. When former increases or later decreases the mixing speed rapidly increases and then drops slowly. The mixing speed arrived at maximum value when the former and the later are 1.44 and 10μm, respectively.