Abstract: Gas permeability of wood is one of the most important physical properties and it reflects the difficulty level of fluid through wood. The permeability of wood can also reflects its drying rate and impregnating treatment effects during modification. The wood gas permeability of I-72 poplar were measured in radial, tangential, and longitudinal by the volume displacement method in this paper. Test results showed that the gas permeability in the radial section was a little bigger than that in the tangential section at same moisture content, and it was a little bigger in the longitudinal section than that in the radial section only at high moisture content.Furthermore, the difference of gas permeability in longitudinal and radial sections will be significantly enlarged along with the moisture content reduction. The permeability differences were not obvious at different position of poplar I-72 in three directions. The permeability increased differently with moisture content decreasing, on this basis, the mathematical equations of the permeability with moisture content changing were built.