Abstract: Mixed grids, composed by structured and unstructured meshes, can be used for adapting to complex geometry problems with lower computational cost than full unstructured grid. The finite volume method is applied to solve the equations of fluid dynanics. The present scheme is tested for the driven cavity problem, where the incompressible fluid is integrated by calculating the velocity fields and computing the pressure field in each time step. Several schemes for unstructured grid are examined, and the compatibility equation is applied to check their consistency. The coupling of different grids is done by overlapping strategy. The computational effort for different size of the domain covering with mixed grid is shown