This thesis are presents results of ground effect on circulation intensity, wing lift coefficient and induced-drag coefficient given by the application af a modified lifting-line method and method of mirror image. Modificated liftingline method is developed as Prandtl’s lifting-line method upgrade for wings with arbitrary geometry. Such method substitutes a 3D wing with a single lifting-line whose elements are bound parts of a horseshoe vortices which all together act as one bound vortex. Intensity of circulation is determined by Biot-Savart law applying boundary condition of tangential flow in control points allocated on a three-quarters of a local chord. That way calculated circulation intensity enables the estimation of a lift coefficient as well as the induced velocity and related induced-drag coefficient at the locus of the lifting-line. Comparison of this method with Prandtl’s and vortex lattice method along with experimental data has been made. It has been shown that modificated lifting-line method gives results in good correspondence with results of above mentioned methods and experiments. The problem of wing aerodynamic characteristics in ground effect is being solved applying the boundary condition of tangential flow at the level of ground. A boundary condition formulated as that allows us to comprehend the ground effect as influence of mirrored wing on a real wing which is placed at the same distance from the ground as a real wing. At the first place the ground effect manifests in reduction of induced drag and then in increase of circulation intensity and lift. Above all other geometric features of the wing, dihedral, aspect ratio and taper ratio are the most correlated with ground effect which points out that ground effect can’t be treat as a unique function of wing height. That leads us to introduction of a lift ground-effect influence ratio and induced-drag ground-effect influence ratio. Both of them combine the geometry of wing and dimensionless h=b ratio that represents a measure of distance between wing and ground. It becomes easy to determine the height of wing at which the ground effect becomes neglectable. It has been shown that in such analysis the starting value of a lift coefficient in ground effect at constant angle of attack should be taken in account. Modificated lifting-line method has been used for estimation of ground-effect influence ratios on a real aircraft with complex planform.