In this paper, switching process of electro osmotic flow is numerically and analytically investigated in a two dimensional Y-shape three-way channel. In this research, it is shown that changing the flow direction through a three-way channel can be simply conducted by varying applied electrical voltage at channel’s ends. In theoretical approach, three equations are introduced to approximate switching voltage ratio and dimensionless flow rate before and after switching process, respectively. These equations are derived base on some simplifying assumptions when distance between output branches and dimensionless double layer thickness parameter are assumed to be flow variables. Numerical simulations are also conducted by using the lattice Boltzmann method to solve all governing equations including the Navier - Stokes, the Poisson - Boltzmann, and the Laplace equations in a 2D three-way channel geometry. Comparison between analytical and numerical results indicates that introduced approximated equations can successfully predict switching voltage ratio and dimensionless flow rate (before and after switching process) by employing considerably lower computational efforts in comparison with numerical approach. In this regard, the introduced semi-analytical equations can be useful for better understanding and to more effectively designing of micro electro mechanics systems.