Due　to　frequent　changes　in　the　humid　and　hot　environment,　the　residual　soil　with　a　particle-size　distribution　(PSD)　from　gravel　to　clay　experiences　multiple　drying-wetting　cycles.　The　pressure　plate　test　and　nuclear　magnetic　resonance　(NMR)　spectroscopy　were　used　to　investigate　the　influence　of　drying-wetting　cycles　on　the　soil-water　characteristic　curve　(SWCC)　and　pore-size　distribution　(POSD)　of　undisturbed　residual　soil.　The　results　showed　that　the　water-holding　capacity　of　the　residual　soil　decreased　as　the　number　of　drying-wetting　cycles　increased　and　gradually　stablilized,　and　then　the　van　Genuchten　(VG)　model　was　found　to　perform　well　on　the　SWCC　during　the　drying-wetting　processes.　The　NMR　results　indicated　a　double-pore　structure,　and　the　porosity　of　the　residual　soil　as　well　as　the　internal　water　content　increased　smoothly　with　more　drying-wetting　cycles.　The　obtained　POSD　curve　of　soil　implied　that　drying-wetting　cycles　had　a　more　obvious　effect　on　small　pores　and　macro-pores　than　on　micro-pores　and　meso-pores.　Theoretical　calculations　evinced　that　the　product　of　the　matric　suction　and　relaxation　time　should　be　constant　at　a　constant　temperature.　However,　the　experimental　results　did　not　effectively　reflect　such　a　relation　between　the　matric　suction　and　relaxation　time.　A　modified　VG　model　based　on　the　cumulative　pore　volume　was　utilized　to　describe　the　POSD　under　drying-wetting　cycles.　Subsequently,　the　proposed　Rational2D　surface　equation　was　used　to　accurately　reflect　the　internal　relationship　between　the　SWCC　and　POSD　curve　under　different　numbers　of　drying-wetting　cycles.　Moreover,　the　fractal　model　for　the　SWCC　derived　from　the　capillary　theory　confirmed　that　the　matric　suction　had　a　strong　linear　relationship　with　the　relative　volumetric　water　content　in　the　log-log　scale.　Also,　the　fractal　dimension　can　be　approximated　as　a　constant,　because　its　attenuation　is　small　with　more　drying-wetting　cycles.