Abstract: A method for generating three-dimensional mixed element type unstructured grids and its application for viscous flow simulations by solving the Navier-Stokes equations are presented.Pirzadeh's advancing-layer method is modified to generate high quality mixed prismatic/pyramid/tetrahedral element type unstructured grids in boundary-layer region,and the traditional advancing-front method is used to construct isotropic tetrahedral grids in the residual flow region.Three-dimensional Navier-Stokes equations are solved by using a cell-centered finite-volume method.A new local time stepping method has been developed to eliminate the adverse influence of grid quality on solve stability and convergence speed.Viscous flow problems around the ONERA M6 wing and DLR-F4 wing-body configuration are simulated to verify the correctness and practicability of the methods presented.