Unsaturated　aeolian　sand　is　the　main　railway/highway　sandy　subgrade　filling　material　in　the　desert　area　of　Alashan,　Inner　Mongolia.　In　recent　years,　the　extreme　climate　events　frequently　happen　in　Inner　Mongolia.　Under　the　extreme　rainfall　conditions　in　the　desert　area,　the　rainfall　infiltration　process　and　the　unsaturated　state　evolution　of　aeolian　sand　subgrade　is　significant　to　the　hydraulic　behavior　distribution　and　the　deformation　development　under　traffic　loading.　In　this　study,　the　SWCC　(soil-water　characteristic　curve)　parameters　of　aeolian　sand　was　firstly　calculated　and　discussed　through　van　Genuchten　model　and　the　linear　approach.　Then　a　unified　framework　was　proposed　to　describe　the　hydraulic　behavior　evolution　of　aeolian　sand　subgrade　under　extreme　rainfall.　Considering　the　effect　of　soil　properties　and　rainfall　conditions　on　infiltration　process　of　aeolian　sand　subgrade,　a　normalized　SWCC　model　was　established.　An　analytical　model　of　maximum　infiltration　depth　for　aeolian　sand　subgrade　affected　by　extreme　rainfall　was　further　developed.　Lastly,　the　numerical　simulation　results　of　the　maximum　infiltration　depth　for　aeolian　sand　subgrade　under　an　extreme　rainfall　event　verified　the　correctness　of　the　analytical　model.　This　research　can　lay　a　foundation　for　studying　the　hydro-mechanical　coupling　behavior　of　sandy　subgrade　in　desert　areas.