Abstract: Fluidization of fluid-particles suspension is simulated using two-fluid model (TFM) and discrete element method (DEM) according to the open source code MFIX-DEM and MFIX-TFM with a low density ratio-based kinetic theory of granular flow (KTGF) in sub- and super-critical water fluidized beds (FB). Both approaches illustrate that a transition fluidization state with wavy-like flow near the bottom and churn-like flow at the upper parts is behaved in subcritical water FB, unlike aggregative fluidization in supercritical water FB. The fluidization is evaluated using three different dimensionless numbers and stability function. Quantitatively, the difference in solid volume fractions, fluid Reynolds stresses and dominant frequencies of volume fraction fluctuations exist between MFIX-DEM and low density ratio KTGF-based TFM in sub- and super-critical water FBs. The simulated fluid volume fractions and expansion heights using a low density ratio KTGF-based TFM agree well with the experimental data in an ambient water FB.