Hydrogen-assisted　cracking　(HAC)　is　a　coupled　phenomenon　between　crack　growth　rate　and　hydrogen　diffusion　to　the　region　ahead　of　crack　tip.　To　understand　the　cracking　mechanism　and　to　control　or　predict　the　HAC　rate,　knowledge　of　hydrogen　diffusion　around　a　crack　tip　is　essential.　Metastable　austenitic　stainless　steels　can　be　severely　embrittled　by　hydrogen　due　to　strain-induced　alpha＇　martensite　transformation　around　crack　tip,　as　the　hydrogen　diffusivity　in　a＇　martensite　is　much　higher　than　in　gamma　austenite　while　the　solubility　is　lower.　However,　the　effect　of　induced　a＇　martensite　on　local　diffusion　of　hydrogen　around　a　loaded　crack　tip　has　not　been　intuitively　demonstrated.　This　study　first　reveals　the　quantitative　relations　of　hydrogen　diffusivity　and　solubility　with　induced　a＇　martensite　amount,　and　then　performs　FE　analysis　of　hydrogen　diffusion　around　a　crack　tip　in　a　304L　ASS　cylinder　storing　high　pressure　gaseous　hydrogen　with　considering　the　combined　effect　of　alpha＇　martensite　transformation　and　hydrostatic　stress　on　diffusion.　The　hydrostatic　stress　exhibits　a　peak　value　at　a　distance　away　from　crack　tip,　while　the　peak　a＇　martensite　volume　fraction　locates　at　the　crack　tip.　Compared　to　the　analysis　only　considering　stress　effect,　the　presence　of　induced　alpha＇　martensite　can　not　only　significantly　accelerate　the　hydrogen　transport　to　the　critical　region　ahead　of　crack　tip,　but　also　markedly　elevate　the　level　that　the　peak　hydrogen　concentration　reaches.　The　peak　hydrogen　concentration　doesn＇t　locate　at　the　peak　hydrostatic　stress　site　as　generally　expected,　but　at　the　site　in　the　gamma　austenite-rich　region　abutting　the　a＇　martensite-rich　region　at　crack　tip　vicinity,　because　this　site　possesses　very　high　hydrogen　solubility　and　close　to　the　high　hydrogen　diffusivity　region,　consequently　accommodating　the　hydrogen　getting　off　the　a＇　martensite　diffusion　＂highway＂.　Copyright　(C)　2016,　Hydrogen　Energy　Publications,　LLC.　Published　by　Elsevier　Ltd.　All　rights　reserved.