Abstarct: The non-dimensional Navier-Stokes equations in rotational form for the two dimensional mixing laxyer flow are solved using direct numerical simulation. The length scale and the velocity scale of the baxse flow at the inlet boundary of computational domain are used as two characteristics to define the flow Reynolds number. These two characteristics are the mixing laxyer half width and velocity difference of two streams. The governing equations are discrete in the stream wise direction (x), using a sixth order compact finite difference scheme, and cross stream direction (y), a mapped compact finite difference scheme, respectively. A tangent mapped of y = β tan(πζ / 2) is used to relate the physical domain in the double infinity of − ∞ < y < ∞ to the computational domain of ζ (−1 ≤ ζ ≤ 1) . The compact third order of runge-kutta method is used for the time-advancement purpose. Four models is used in outflow boundary condition to create a non-reflective type boundary condition at the outlet then we changed the mixing laxyer structure and found the best model for mixing outflow boundary condition in different structures.