In recent years, with the advances made in the technology of manufacturing micro systems, the use of these systems has grown dramatically . On the other hand, the use of electro-osmotic as a means for creating flow and improving mixing in microchannels is increasing. Mixing phenomenon is one of phenomena that not completely occur in microchannels due to some reasons such as low Reynolds number of the current flow (laminar flow), consequently requires the use of micromixers in these systems. In this study, mixing in combined electroosmotic-pressure driven flow through an annular microchannel due to electrokinetical effects in axisymmetrical flow was investigated qualitatively and quantitatively. For this purpose, two fluids in liquid phase with two different concentrations of same chemical species are studied and numerically investigated. The basic fluid is the electrolyte, which flows in an axisymmetrical microchannel with electric charging walls. For thorough simulation of electro-osmotic flow in the heterogeneous microchannel, the coupled equations of Navier-Stokes, Nernst-Planck, Poisson and the concentration equation are respectively solved for fluid motion, ionic concentration distribution, electric field distribution, and concentration. The effect of parameters affecting mixing such as field intensity, pressure gradient, wall heterogeneity properties and their arrangement, etc. have been investigated. In this research, suitable concepts for the study of mixing have been introduced and the mixing phenomenon within the micromixer has been studied by using them. The achievements of this study indicate that the asymmetric degree of the flow field pattern is the key parameter for enhancing the mixing performance. This achievement can be used to design micromixer in laboratory chips. Keywords: Electro-osmotic, Microchannel, Electric field, Micromixer