In this paper, the relationship between sound absorption properties of porous metal-fiber material with inner cavity, and the kind of inner medium, depth and position of cavity is studied. The results show that as medium is air the average absorption coefficient of is 0.62 which is higher than 0.58, that of structure without cavity. But as the cavity filled with sulfate the average absorption coefficient goes down to 0.52. As the depth of cavity increased from 3.5 mm to 6mm, the average absorption coefficient also increased from 0.53 to 0.56 with absorbtion band broadening. The closer of the distance from cavity to absorption surface, the better properties of sound absorption are gained. For the inner structure with many dispersed cavities, the absorption properties of material may be further improved.