The patterns of primary flow jet core in steam ejector were investigated using computational fluid dynamics (CFD) method. Simulations based on ideal gas model at different operating conditions were performed. The results demonstrate the pattern of primary pseudo-shock flow was affected by the operating conditions obviously when value of operating condition was bigger than that of the critical condition. Compared with the results generated from ideal gas modelling, the primary pseudo-shock flow predicted by wet steam model has a similar pattern and almost the same effective area. But the wet steam model based simulation gives a further downstream choking position and a higher secondary fluid flow velocity at choking position. The above two factors lead to improved entrainment ratio (E-m) and increased critical back pressure of steam ejector compared to the results generated from ideal gas modelling. More importantly, the wet steam model predictions show better agreement with the experimental data. (C) 2018 Elsevier Ltd. All rights reserved.