Abstract: The process of shock acted on a vibration and shock isolation system with double-stiffness was divided into two steps. In the shock action phase of a half sine wave, the response was calculated by using a double DOF model. In the free vibration phase, the response was calculated by adopting a single DOF system, the initial displacement and velocity of single DOF adopt the final value of the first phase. The property of the double-stiffness system in the shock of the half sine wave was analysed by using this method. Some conclusions were gained by being compared with the linear system. Results indicate the preferable effect of vibration and shock.