Abstract: On basis of concepts of population and adaptive degree, anew method is proposed to identifyparameters in the constitutive model used to improve Particle Swarm OptimizationAlgorithm starting from a stochastic solution. This method can solvedifficult problems of identifyingparameters in a constitutive model for hardening rubber-like materialswith large strain. Firstly, by a constitutive model test of uniaxial tension, a point of inflexion in the experimental curve is obtained, the PSO is used toidentify the parameter, and then the result is testified by a simpleshearing test. The result shows that the PSO method enjoysefficiency, high precision and quick convergence,in identifying constitutive parameters and it canbe widely used for various complex materials.