A method for generating three-dimensional unstructured viscous grids automatically is presented. High-aspect-ratio and anisotropic tetrahedral grid cells are constructed in viscous dominated flow regions by advancing-layers method (ALM).When the height of viscous grids reaches the requirement,the conventional advancing-front method (AFM)will generate isotropic grids to fill the remained flow regions.By the control of stretched function and background information,the transition from grids generated by ALM to isotropic grids generated by AFM becomes smooth and gradual.The unstructured viscous grids of M6 wing and the simple flow results of corresponding Navier-Stokes solution based on the present grid are also provided.