Abstract:This paper studies the mechanism and origin of linear flow components (viscous flow and slip flow, or Knudsen diffusion) and nonlinear flow component, which occur in fluxes of the compressible fluid permeating through wood. The viscous flow exists in all the capillaries which the fluid flows through, and the slip flow only exists in those whose dimension of pore crosssection is equal to or less than mean free path of fluid molecule. Due to kinetic energy loss at the entrance and exit of a capillary, the nonlinear flow may be brought about when the compressible fluid permeate through wood. In case of the occurrence of the nonlinear flow, Darcy‘s and Poiseuille‘s laws are no longer applicable to the permeating flow. One must affirm whether there is the nonlinear flow and avert its effect on the permeability when calculating the wood fluid permeability and equivalent radius of the capillary by means of Klinkenberg equation and Adzumi equation with the measurement data. There is relationship in some degree between wood permeability to compressible fluid and flow pattern of the permeating fluid.