Wing-in-ground effect (WIG effect) is the phenomenon caused by the near-ground flight of a wing. This phenomenon results in the increase of wing lift and the reduction of induced drag. This phenomenon is expected to be applied to develop wing-in-ground craft that could have good aerodynamic characteristic and operate at high speed. Aerodynamic analysis plays an important role in the design of WIG craft. In this paper, numerical and experimental studies are carried out on a 3D wing of Clark-Y airfoil. Three dimensional Computational Fluid Dynamics (CFD) simulations of the wing are performed at various heights to chord ratios (hie), ranging from 0.05 to 1 and different angles of attack (AGA), varying from 0 to 10°. The simulation conditions are established quite similarly as the experiment conditions with subsonic wind tunnel. The simulated results about aerodynamic coefficients are in good agreement with the experimental results measured in wind tunnel. The wing-in-ground effect in both 20 and 3D cases are clarified.