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.