Taking into account the nonlinear, characteristic of the pre-pressing spring, the equivalent mechanics model of a giant magnetostrictive material (GMM) transducer is set up in the paper, which is based the dynamic experiment of GMM and the influence of unsymmetrical piece-wise linear stiffness of the pre-pressing spring. Based on, the one-freedom-degree vibration model of a GMM transducer, unsymmetrical piece-wise linear nonlinear characteristic from pre-pressing spring is investigated. By the analysis of KBM method, the first order harmonic motion component of the GMM transducer is obtained. By the numerical simulation, the complicated bifurcation and chaos behavior of the vibration system with the, unsymmetrical piece-wise linear are founded which need to be taken accounted in the design of GMM transducer.