This paper analyze the variation of the inertial parameters of the powertrain based on the orthogonal test, and their effect on the vibration characteristics of the system. Then the paper designs a test plan of the two levels orthogonal test with 6 facts by establishing a mathematical model of 6-dof in engine-mount system. We spend 8 times having done the orthogonal computation with MATLAB. The experiment results bring us the average of the changes of two levels decoupling owned by the mounting system's 6 rank inherent characteristics on each direction .And this changes are caused by the fluctuating of inertial parameters. Finally, we analyze the variation of the rotational inertial and the inertial integrated parameters, and their influence on the quality level of the sensitivity on the all decoupling parameters in engine-mounting system on each direction. Combined with the calculation examples in the thesis, we discuss the individual inertial parameters of the engine-mounting system ，which is the crucial design parameters of sensitivity analysis, and have provided a parameter basis for the design of engine-mounting system.