For the reduction of the electromagnetic field impact on the parameters of electronic equipment it is used shielding in many different shapes and quality. The quality of the shielding is dependent on size, shape and amount of the openings in the body of the shield. In the electromagnetic immunity and emission tests it is very difficult to predict the shielding efficiency from theory of the refraction, reflection and diffraction due to the very complicated shape and material mix in design configuration for multilayer PCB, supports, covers and screens. For this reason we propose to use drawn 3D electromagnetic model to build up and realise calculation of scattering matrix parameters as the estimation of the shielding efficiency in the given frequency range