Abstract: To overcome the defects of composite method on the moment of inertia existed in the large commercial software and experiment,using the matrix deduced the theorem of moment of inertia of multi-body.Vector is replaced by coordinate array to establish the relationship of the same vector array between coordinates;the theory of linear algebra is used to deduce the relationship of inertia matrix between coordinates to establish the relationship of the moment of inertia and product of inertia between coordinates.The conclusion is extremely concision,easy to develop the corresponding program with computer language.Now composite software of moment of inertia is developed by using the method.The software that can composite the mass,the center of mass and moment of inertia of the two rigid bodies does not need to establish rigid body model,only need to input the basic parameters on it.Moment of inertia of composition is preliminary work of dynamics analysis for automotive powertrain system,which has obtained the good result in decoupled optimization of automotive powertrain mount system.

Key words: multi-body, moment of inertia, product of inertia, composite method, automotive powertrain