Abstract: Research in this essay is about the propagation characteristics of the Lamb waves in porous functionally gradient materials (FGMs). With the help of eigenfunction expansion method and the relationship between elastic constants with porosity, this essay discusses phase velocity dispersion curves of the Lamb waves in iron-based alumina FGMs of finite thickness under different porosities. It also analyses the effects of porosity on the phase velocities of the Lamb waves in iron-based alumina FGMs. The results validate that the dispersion curves for Lamb waves can reflect the information of elastic modulus, Poisson ratio, density and porosity in FGMs, the conclusion can be useful to study inverse properties of porous layered materials.