We have developed a technique for estimating damped vibration of automotive body panels with sound-proof structures. It calculates damping properties for sound-proof structures involving elastic body, viscoelastic body and porous media. For elastic and viscoelastic body displacement are modeled using conventional finite elements including complex modulus of elasticity. Both effective density and volume elasticity have complex quantities to represent damped sound fields in the porous media. Particle displacement in the media is discretized using finite element method. Displacement vectors as common unknown variables are solved under coupled condition between elastic body, viscoelastic body and porous media. Further, explicit expressions of modal loss factor for the mixed structures are derived using asymptotic method. Eigenvalue analysis and frequency responded were calculated for automotive panels laminated with viscoelastic body and porous media using this technique, the results almost agreed with the experimental results.