Abstract: Utilizing Galerkin method, the finite element equation of acoustic interaction between two media is established. Based on the empirical equations of porous material considered as a fluid, the rules between the complex speed&density and flow resistivity are analyzed. According to the finite element equation and the empirical equations, two different porous material structures transmission loss(TL) versus the flow resistivity are attained. The results showed that the TL of air cleaner will increases with the increase of flow resistivity, but the TL of resistance muffler has a complicated change and exists a maximal value within the calculation frequency.