Under an applied magnetic field, the Faraday magnetic-optical effect of composite media is dependent on the calculation of dielectric tensor. It is rather complicated to evaluate the dielectric tensor of composite media. Using the inhomogeneous composite effective electric field equal to the average electrie field the effective-medium approximation equations of the inhomogeneous composite are derived. By use of dielectric tensor εe equation and self-consistency condition, the grain films systematic formula of magnetic-optical Faraday rotation angle is calculated. Corresponding matrix, ion concentration and the shape of metallic granular in grain films with Cu as example, the influence for magnetic granular films Faraday rotation angle is discussed. The effective medium approximate calculation is consistent with experimental result.