Abstract: Based on the 6 degrees of freedom(DOFs) vibration coupling model of the powertrain mounting system, the sensitivity analysis method was used to calculate the sensitivity of each natural frequency to the mounting stiffness in each direction. It is to identify the key rubber stiffness that affects the vibration in a certain direction, and to provide a theoretical guide for the improvement of the vibration characteristics in a certain direction. Then, taking the decoupling rate of each direction as the objective function, considering the drive shaft excitation, the sensitive vibration frequency region of the human body and the each direction vibration coupling conditions for the optimal constraint condition determination, a optimization algorithm was used to extract the optimal stiffness value of each direction and to improve vibration isolation performance of the mounting system. Aiming at the vibration deterioration of a certain powertrain system, a mounting system was designed by means of the sensitivity analysis method and vibration energy decoupling method. Finally, a vibration bench test was applied on the mounting system to verify the availability of the optimization design.