A discrete phase simulation is conducted to study the bubble and particle dynamics in a three-phase fluidized bed at high pressures. The Eulerian volume-averaged method, the Lagrangian dispersed particle method, and the volume of fluid (VOF) method are employed to describe, respectively, the motion of liquid, solid particles, and gas bubbles. A bubble-induced force model, a continuum surface force (CSF) model, and Newton's third law are applied to illustrate, respectively, the coupling effect of particle-bubble, gas-liquid, and particle-liquid interactions. A close-distance interaction (CDI) model is included in the particle-particle collision analysis, which considers the liquid interstitial effect on colliding particles. Effects of the pressure and solids holdup on the bubble rise characteristics such as the bubble rise velocity, bubble shape and trajectory are examined. Simulations of the bubble rise velocity at various solids holdups and pressures are conducted along with the maximum stable bubble size and the particle-bubble interactions. The simulated results compare favorably with the experimental data and calculation from a mechanistic model.