1. A method for simulating a rubber material comprising the steps of: setting a rubber material model modeled on a rubber material including a matrix rubber, silica, and an interface bonding agent to bond them with numerically analyzable elements; calculating deformation by setting conditions in said rubber material model; and acquiring needed physical quantity from said deformation; calculation, wherein said rubber material model comprises; a matrix model modeled on the matrix rubber; a plurality of silica models modeled on said silica arranged in said matrix model; and an interface model surrounding annularly each of said silica models and having a harder physical property than said matrix model, wherein said rubber material model comprises a coupled body formed by coupling a plural of said silica models via said interface model, and wherein said step of setting the rubber material model comprises a parameter determination process to determine a parameter of physicality in said interface model, the parameter determination process comprising the steps of: preparing at least a first unvulcanized rubber composition having the same compound as said rubber material model of an analysis object, and a second unvulcanized rubber composition having a compound excluding an interface bonding agent from the first unvulcanized rubber composition; obtaining first and second residues after removing the matrix rubber from the first and second unvulcanized rubber compositions, respectively, by immersing the first and second unvulcanized rubber composition into a solvent; estimating a difference between two peak temperatures T 2 −T 1 by measuring at least a peak temperature T 2 of loss tan δ of said second residue and a peak temperature T 1 of loss tan δ of said first residue; preparing a basic vulcanized rubber material having a compound excluding silica from said first unvulcanized rubber composition, and different kinds of vulcanized rubber materials having a difference only in crosslink density from the basic vulcanized rubber material; obtaining a relation between said peak temperatures T 2 and T 1 of loss tan δ of the vulcanized rubber material and the crosslink density by measuring each of the peak temperatures T 2 and T 1 of loss tan δ of said vulcanized rubber materials; specifying a crosslink density of the vulcanized rubber material having a peak temperature of loss tan δ is equivalent to a temperature obtained by adding said difference between two peak temperatures T 2 −T 1 into a peak temperature T 3 of loss tan δ of said basic vulcanized rubber material from said relation; and defining said parameter of said interface model on the basis of the physicality of the vulcanized rubber material of said specified crosslink density.