A simulation method of estimating performance of a product made of a viscoelastic material, comprising the steps of measuring a value of a strain, a strain speed, and a stress generated in viscoelastic material momently in a measuring condition equivalent to a state in which the product is actually used; deriving time history data of a viscosity resistance of the viscoelastic material separately in each of a strain increase state and a strain decrease state from time history data of the strain, the strain speed, and the stress and a viscoelastic model set in consideration of a viscosity of the viscoelastic material; setting the product as a product model whose performance is analyzed and inputting a relationship among the strain, the strain speed, and the viscosity resistance to the product model to conduct a simulation in consideration of a phenomenon that the viscosity resistance changes in dependence on a variation of the strain and the strain speed and in consideration of a difference in the viscosity resistance between a strain increase state and a strain decrease state.