A variety of complex dynamic load can cause the ship isolator to produce large displacement when the ship during the voyage, which makes the below air-bag have a greater deformation.Usually, air-bag vibration isolation system with an elastic constraint is used to restrict the maximum displacement of supported equipment.In this paper,based on the method of theoretical dynamics a nonlinear dynamic model of air-bag with a displacement restrictor is developed, which includes a clearance between the linear springs.