1. A computer-implemented simulation method for a macromolecular material and filler, comprising: a process in which a polymer model of a macromolecular chain of the macromolecular material modeled by a plurality of particle models is defined; a process in which a filler model of at least an outer surface of the filler is defined; a simulation process in which a molecular dynamics calculation is performed using the filler model and the polymer models disposed in a space; an interface-layer-thickness calculation process in which, the thickness of an interface layer formed between the filler and the bulk of the macromolecular material and having a dynamic property different than that of the bulk, is computed from results of the simulation process, wherein the interface-layer-thickness calculation process comprises a process in which the space in which the polymer models are disposed is partitioned into a plurality of domains bounded by boundary surfaces along said outer surface of the filler, a relaxation modulus calculation process in which relaxation moduli of the domains are computed, and a determining process in which the thickness of the interface layer is computed based on a variation of the relaxation moduli of the domains; a material property calculation process in which a material property of the macromolecular material with the filler is computed by defining conditions including the computed thickness of the interface layer on the space in which the polymer models are disposed; and a material property judging process in which it is judged whether the computed material property is within an allowable range or not, wherein if the computed material property is outside the allowable range, the conditions defined on the space are changed, and the simulation process, the interface-layer-thickness calculation process, the material property calculation process and the material property judging process are repeated, and if the computed material property is within the allowable range, the macromolecular material with the filler is manufactured based on the conditions defined on the space in which the polymer models are disposed.