The existing of voids is the character of the porous media
which determine the constitution relation of porous media will be more complicated. A model of ideal porous media is presented. The apparent stress and apparent strain
actual stress and actual strain of skeleton for porous medium are defined. A discussion of the stress-strain relationship of the ideal porous medium suggests that although skeleton structure could be satisfied with the hypothesis of stress-strain linear elastic
the relationship between apparent stress and apparent strains remains nonlinear character. The nonlinear relation of stress and strain is the character of porous media.