Abstract:The overlayer model is a powerful library of rheological models,and the procedure of determining the parameters of the overlayer model is also the procedure of identifying the constitutive relation. Based on this model,a novel approach of identifying the rheological constitutive relation of engineering material,is introduced to overcome the deficiency of the traditional identification procedure which relies too much on specific models. The nonlinear optimistic initial values of design variables are selected by analyzing the sensitivity of these variables with object function,then the deficiency of easily falling into local extreme point during the determination of parameters of rheological constitutive model is avoided effectively. A selection scheme of initial value in nonlinear displacement back-analysis(combined with the FEM and the complex optimization method) is also proposed.