Micro-fluidics is an area of science and engineering in which the behavior of fluid is different from the predictions of the conventional flow theory. If the hydrodynamic diameter of a channel is comparable with the mean free path of the gas molecules moving inside the channel, the fluid can no longer be considered to be in thermodynamic equilibrium and rarefaction effects can occur. To avoid enormous complexity and extensive numerical cost encountered in modeling of nonlinear Boltzmann equations, the Navier-Stokes equations can be solved considering the concepts of slip flow regime and applying slip velocity boundary conditions at the solid walls. This paper presents the simulation of the laminar incompressible fluid flow through micro-channel over the slip flow regime and the appropriate boundary condition is implemented by means of a user defined function routine into finite volume solver Fluent. Three different Knudsen numbers have used to investigate the effects of rarefaction.