Abstract: In order to study the influence of anisotropy air voids structure in porous asphalt mixture on seepage characteristics，the theory of Darcy Law was adopted． Air voids micro-distribution characteristics of porous asphalt mixture are obtained on the basis of industrial CT，seepage flow numerical model of porous asphalt mixture is estab-lished and the internal flow characteristics of water within porous asphalt mixture are analyzed by the finite volume method． In the meantime，a cuboid test-piece is designed as a representative volume element to describe the anisot-ropy permeability performance of the porous asphalt mixture． The results demonstrate that the porous asphalt mix-ture features an uneven distribution in light of air voids，denser connecting air voids and larger area per single air void in horizontal direction than that in vertical direction． The results also indicate that because of the anisotropy of air voids，the permeability performance of the mixture sample also features anisotropy，the permeability coefficients in two horizontal directions tend to be very close，which are about two times those of the vertical directions． Thus in terms of the analysis of the permeability performance，the porous asphalt mixture can be considered as isotropy hori-zontally or as anisotropy when analyzed both horizontally and vertically．

Key words: road engineering, porous asphalt mixture, anisotropy, air voids structure, permeability, permeabi-lity coefficients