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.