A hybrid isolator consisting of a giant magnetostrictive actuator(GMA) and an air spring is presented in this paper. The nonlinear dynamic model of a two-stage vibration isolation system applying this type of hybrid isolator on a flexible foundation is established based on first magnetoelastic theory and Stone-Weierstrass theorem. The relation between the variation of nonlinear parameters and the amplitude-frequency response characteristic curve of the isolation system is researched by numerical simulation. And the influence of exciting current of GMA on isolation effect of the system is investigated as well.