Abstract: This paper presented types and mechanisms of the compressible fluid such as air flow through wood. The slip flow and factors affecting the compressible fluid flow through spruce (Picea jezoensis var. komarovii) and pine(Pinus koraensis) woods along grain direction were measured over a rangeof the reciprocal average pressure from 1.4 to 48 atm^-1. The slip flow wasobserved in the air permeability of woods of the two species mentioned above,however, the slip flow component of spruce wood was higher than thatof pine. The slip flow percentage of viscous flow (K_S/K_T%) and the ratio ofspecific superficial air permeability to the true permeability (K_G/K_T) at 0.5atm, as well as the slip flow factor b were calculated as 69.39%, 1.69 and0.356 atm respectively for spruce wood and 37.64%1.36 and 0. 197 atm for pine.The slip flow was inversly proportional to effective capillary radius of woodtrue permeability and average air pressure.

Key words: Picea jezoensis var komarovii, Pinus koraensis, Slip flow, Fluid permeability