A statistical mechanics of long chain molecules has been used as an alternative to the continuum mechanics approach to develop constitutive model of the soft tissue. By this method, molecules are assembled and represented in a unit cell that is the basic element of network model. Regarding to the latest developed network model which is called eight-chain model, a unit cell consists of eight chains. Each long-chain is composed of a number of rigid links, and represents a collagen fiber. In nonlinear modeling, the Langevin function is employed as a statistical function to determine the length of chainss after deformation. There are five parameters, that is, the density of the constituent molecule chains, the bulk modulus, and the height, width, and depth of the unit cell, necessary to characterize mechanical property of material. However, wever, the relationships of parameters to constitutive equation are not fully understood. The purpose of this study is to investigate and understand the significance of these five material parameters to the constitutive law, based on simulation results.