A discrete phase simulation (DPS) is conducted to investigate multi-bubble formation dynamics in gas-liquid-solid fluidization systems. A numerical technique based on computational fluid dynamics (CFD) with the discrete particle method (DPM) and volume tracking represented by the volume-of-fluid (VOF) method is developed and employed for the simulation. A bubble-induced force (BIF) model, a continuum surface force (CSF) model, and Newton's third law are applied to account for the couplings of particle-bubble, bubble-liquid and particle-liquid interactions, respectively. A close-distance interactive effect between colliding particles is considered in the formulation of the particle-particle collision model. Two-dimensional simulations of the behavior of bubble formation from multi-orifices in liquids and Liquid-solid suspensions are conducted at high pressures up to 19.4 MPa under constant gas flow conditions. Experiments are also conducted in this study to quantify the bubble formation behavior from a single orifice under comparable gas flow conditions. The study indicates that the liquid flow dynamics induced by adjacent bubbles and bubble wake significantly affects the multi-bubble formation process. The simulation results on the initial bubble size and bubble formation time under various pressures and solids hold-up are found to be in good agreement with those obtained experimentally as well as those predicted based on the analytical model developed earlier by the authors.