Abstract A CFD-ABND coupling model was used to study the flow characteristic of gas-liquid two-phase flow in the process of gas passing through the liquid bath of a water-coal-slurry entrained-flow gasifier. In this model, an average bubble number density (ABND) approach was employed and merged with the two-fluid model. A two-phase version of the RNG k-ε turbulence model was used for the liquid and gas, respectively. Comparisons of computational results with experimental data are done. The results show that the gas gathers along the outer wall of the cooling pipe and rises. The higher turbulent kinetic energy of gas and liquid, the larger bubble and the higher interfacial area concentration exist mainly near the exit and outer wall of the cooling pipe. The existence of a separator inserter is very helpful to strengthen the turbulence between gas and liquid; this can reduce the bubble diameter and increase the interfacial area effectively.