Based on typical characteristic of linear elastic,plateau and densification zone for common plastic foam, the effective constitutive relationship was proposed. Then functionally graded foam sturcture was introduced , and dynamic model of the cushioning system was built. The effects of gradient functiontions ,density difference, and incident energy on the impact response of the functionally graded foam structure were explored by using Range-Kutta method.The results reveal the functionally graded foam is efficient to the smaller incient energy conditions, which extend the range of protection against impacts.