Abstract: The possible intermittent impacts of a two-stage isolation system with rigid limiters have been investigated. The isolation system is under periodic external excitation disturbed by small stationary Gaussian white noise after shock. The maximal impact Poincar map is proposed based on the multi-body dynamics with unilateral constraints. Then in the period after shock, the zero order approximate stochastic discrete model and the first order approximate stochastic model were developed. The real isolation system of an MTU diesel engine was used to evaluate the established model. After calculating numerical example, the effects of noise excitation on the isolation system were discussed. The results show that the property of the system is complicated due to intermittent impact. The difference between zero order model and the first order model may be great. The effect of small noise is obvious. The results may be expected useful to the naval designers.