The 3-dimensional straight wing (NACA0015 airfoil) flying over wavy ground at high grade sea condition was studied numerically by adopting the computational fluid dynamics (CFD) method. The NS equation of unsteady incompressible flow and second order RNG k-ε turbulence model were solved in Fluent. First, the necessity of involving local wind speed and velocity of wave when researching qavy-ground-effect numerically was investigated with 2dimensional cases. Besides, the trends and reasons that aerodynamic coefficients vary with ground clearances under wavy-ground-effect were studied. Then, the aerodynamic force and the rolling moment of 3-dimensional airfoil were analyzed when the course angle between the direction of flight and local wind speed were different, and detailed description of the causes and characteristics of the rolling moment were made. After numerically researching these cases, the impact of wavy-ground-effect at high grade sea conditions on the airfoil was illustrated preliminarily, providing basic theory to aerodynamic design and flight control for WIG craft.