The　fluidization　behaviors　of　Geldart-A　and　B　particles　in　high　pressure,　sub-critical　and　supercritical　water　were　investigated　experimentally　with　the　conditions　of　pressure　up　to　27.2　MPa　and　temperature　up　to　482　degrees　C.　Minimum　fluidization　velocity　was　determined　by　measuring　pressure　drop.　Minimum　bubbling　velocity　was　obtained　not　only　by　analysis　of　the　experimental　differential　pressure　fluctuation　signals,　also　by　the　relationship　between　bed　voidage　and　superficial　velocity.　Correlations　for　the　minimum　fluidization　velocity,　homogeneous　bed　expansion　rate　and　the　minimum　bubbling　velocity　were　proposed.　Transitions　of　fluidization　regimes:　fixed-homogeneous　(F-H),　fixed-homogeneous-bubbling　(F-H-B)　and　fixed-bubbling　(F-B)　were　uncovered　at　temperature　from　ambient　to　supercritical.　The　fluidization　of　F-H　was　found　when　discrimination　number　D-n,　is　below　1.2　x　10(4),　and　the　fluidization　of　F-H-B　was　found　when　discrimination　number　D-n　is　between　1.2　x　10(4)　and　6　x　10(4),　the　fluidization　of　F-B　was　found　when　discrimination　number　D-n　is　above　6　x　10(4).　These　results　are　very　useful　for　the　design　of　the　high　pressure,　sub-critical　and　supercritical　water　fluidized　bed.　(C)　2016　Elsevier　B.V.　All　rights　reserved.