Experiments on the gas-liquid-solid mini-fluidized beds with sizes of 1.45 and 2.3 mm show that the bed diameter has a considerable effect on the phase holdups and gas bubble size, because the macroscopic dimension (macro-scale) in a mini-fluidized bed is close to the dimensions of bubbles (meso-scale) and particles (micro-scale). Hence, the parameter of bed diameter was introduced through the modifications on the energy-minimization multi-scale (EMMS) model for the conventional three-phase mini-fluidized beds to predict the flow behavior of three-phase mini-fluidized bed. These modifications include two correction factors for the liquid and bubble slip velocities and a constraint condition on the bubble coalescence. The correction on the liquid slip velocity is to estimate the effect of column shear stress on the distribution of liquid velocity. The other correction factor is for quantifying the column resistance on the bubble rise. The correction factors were determined by the empirical correlations obtained from the experiments. Similarly, the bubble coalescence constraint is a correlation on the bubble spacing under steady state condition and determined from the experimental data. The modified meso-scale model equations were closed by this constraint condition and the solution of the model met the principle of energy minimization. The model predictions and experimental data agree well within the investigation range of experimental conditions. (C) 2018 Elsevier Ltd. All rights reserved.