The giant magnetostrictive actuator works at high frequency, and then the loss of giant magnetostrictive actuator includes magnetic hysteresis loss, eddy currency loss, and excess eddy current loss of actuator loop. The coupling between four fields (i.e., magnetic field, electric field, thermal field and mechanical stress field) is occurred at the actuator. Considering the mass of Terfenol-D rod, pre-stress, biased field, the loss of magnetic hysteresis and eddy current, a 3-D nonlinear dynamic model of GMA was established based on the coupled relationship of the three fields (magnetic field, electric field and mechanical stress field). The magnetic behavior was described by the Berqvist and Engdahl stress dependent magnetic hysteresis model for ferromagnetic hysteresis. The simulation results with commercial software FEMLAB were in agreement well with the experimental data. Therefore, the model constructed is valid, and it can help to optimize design of the GMA.