In order to reduce the number of numerical meshes and simplify aperture array modeling, an equivalent method of modeling aperture array in which the size effect of apertures is taken into account, is presented in the paper. In this method, the aperture array is replaced by a single aperture which has the same area as the original aperture array, then the scaling factor of the aperture is obtained according to the number of apertures. The empirical relations between the number of apertures and scaling factor are proposed based on theoretical derivation and curve fitting method respectively. The comparison with the commercial software HFSS indicates that the formula based on curve fitting method has a higher accuracy. The applicability of the method is verified by varying the interference source, monitoring point, total area and position of aperture array, shape of aperture and cavity size. As shown by the numerical results, the equivalent modeling approach can significantly reduce the number of meshes, which can serve as a simplified approach to numerical simulation of shielding characteristics of complex cavity.