This paper studied the nonlinear properties of a two stage isolation system with rigid limiters.A discrete model was derived based on the multi-body dynamics with unilateral contacts,and an approximate map was obtained after using the perturbation techniques.By using the above methods,we investigated how the two stage isolation system of a MTU diesel engine responded to external impact.The investigation shows that the system presents complicated nonlinear properties due to impact,and the weak nonlinear part,which could be omitted under no limiters case,may influence the property of the vibroimpact system greatly.Thus the conclusions offers a theoretical reference for designers.