The use of the hydraulic mount and sub-frame (engine cradle) for passenger car is increasingly becoming common in the automobile industry because they can provide excellent frequency and amplitude response characteristics compared to the conventional elastic rubber type engine mount. The 14-degree-of-freedom dynamic model of engine and sub-frame mount system is developed in this paper. The method to solve second-order-differential equation which include variable stiffness and damping is given. A lot of calculation and measurement of vibration response are carried out. It is shown that hydraulic mount and sub-frame mount can effectively isolated the vibration transmitted from engine to body.