Abstract: In order to explore the black-box details of the FLOW-3D bubbly flow model, the effect of the model parameters including the critical Weber number, critical capillary number, initial bubble diameter, drag coefficient, and Richardson-Zaki coefficient multiplier are investigated based on the experimental data of uniform flow in a 45° steep chute. It is discovered the bubble size is dominated by the critical capillary number, whereas the critical Weber number only exhibits a certain effect near the aerated flow surface. The drag coefficient and Richardson-Zaki coefficient multiplier have a significant influence on simulation results, while the effect of the critical capillary number, the critical Weber number and the initial bubble diameter is relatively negligible. A drag coefficient or Richardson-Zaki coefficient multiplier more than the default value will enhance the turbulence and thereby increase air entrainment, and values less than the defaults have even more significant effect. Therefore, when aerated flow is simulated by using FLOW-3D, more attention should be paid to the calibration of the drag coefficient and Richardson-Zaki coefficient multiplier to improve model accuracy.