Parametric modeling and modal analysis for the complex mechanical structure

3D solid models of three elements of a military diesel engine, block, crankshaft and cylinder-head are built separately by using feature technology and parametric technology, and then assembled into combined structure model. The parametric solid model based on the combined structure model is built by using dynamic sub-structure method, and then analyzed its finite element mode. Virtual materials are introduced to simulate the stiffness and damping features of the joint surfaces among the three elements, for those features are difficult to obtain either theoretically or experimentally. Properties of the virtual materials are gradually modified until the finite element method modes results come consistent with the experimental ones. The contrast results show that the parametric model of the combined structure is correct and it can settle the foundation of the further research on the engine's dynamic simulation.