Incorporating an electric propulsion system into conventional vehicle electronic architecture makes electromagnetic compatibility (EMC) become one of the most important issues during electric vehicle design. Electromagnetic shielding is one of the compulsory preventions to protect electronic circuits against electromagnetic interference (EMI). However, apertures of the shielding enclosure reduce shielding effectiveness (SE) by permitting EMI leakage to affect the electronic circuits. When the dimensions of the enclosure remain fixed and the aperture has a particular area, studies such as optimization of the aperture dimensions or changing the enclosure material are essential. In this study, a genetic algorithm (GA) is designed initially, which improves SE by determining aperture dimensions on the front surface of the shielding enclosure. Then, obtained aperture dimensions are used in a numerical model in which the inner surfaces of the enclosure are coated with graphene sheets. It is observed that SE simulation results are in good agreement with measurement ones.