On some occasions

multiple physical or chemical interactions between the fluids and solid skeleton in porous media may take place. Adsorption of fluids is a kind of phenomenon of these interactions. During these interactions

conversion or transfer among kinds of forms of energy take place concomitantly. In this paper

swelling of media caused by fluids in the pore is supposed to be the result of energy inversions from fluids to the media skeleton. Based on this cognition

Miao’s humidity stress field theory is proved theoretically using the first law of thermodynamics and the general method of constitutive theory. Then the applicable conditions and physical meaning of the humidity stress field theory are analyzed. It can be concluded that humidity stress field theory builds a mathematical material which is the idealization of real matter in the manner of the classic elastic theory does.