The　diffusivity　of　concrete　is　closely　related　to　the　microstructure　which　involves　the　interfacial　transition　zone　(ITZ)　between　aggregate　particles　and　cement　paste　at　the　meso-scale,　as　well　as　the　microstructure　of　cement　paste　itself.　At　the　micro-scale,　the　cement　paste　and　the　ITZ　can　be　assumed　to　be　composed　of　an　intrinsic　cement　paste　phase　and　a　pore-water　inclusion,　with　different　porosities.　Under　external　mechanical　stress,　the　porosities　and　the　connectivity　of　capillary　pores　within　the　cement　paste　and　the　ITZ　will　be　changed,　resulting　in　the　change　of　the　chloride　diffusivity　of　concrete.　In　this　study,　a　multi-scale　analytical　method　that　can　predict　the　chloride　diffusivity　of　concrete　subjected　to　low-level　stress　is　proposed.　The　quantitative　relationship　between　the　apparent　diffusion　coefficient　of　concrete　and　the　mechanical　stress　(herein　i.e.　the　volumetric　strain)　as　well　as　the　current　porosities　of　cement　paste　and　the　ITZ　is　evaluated.　The　main　parameters　in　the　analytical　method　are　the　capillary　porosities　of　cement　paste　and　the　ITZ,　the　mechanical　properties　of　the　intrinsic　cement　paste　phase　and　the　aggregate,　the　volume　fractions　of　aggregate　and　the　ITZ,　and　the　mechanical　stress.　A　good　agreement　between　theoretical　results　and　available　test　data　illustrates　the　reliability　and　accuracy　of　the　developed　analytical　approach.　Based　on　the　presented　analytical　method,　the　effect　of　micro-　/　meso-structure　of　concrete　on　its　apparent　diffusivity　was　investigated.　©　2017,　Engineering　Mechanics　Press.　All　right　reserved.