The 2D axisymmetric, real gas model was developed to calculate the ejector in the ejector cooling system. The calculation of the real gas model occupies more computer resources, but its result can be more authentic. The CFD model was validated with available experimental data. Predictions at the operating conditions in the ejector cooling system were discussed. The aim of the prediction is to obtain the ejector performance in the non-design condition and variable operating condition. There is an optimum evaporator condition te=20°C (Pe=0.65bar) with the giving geometry parameters. In the calculation range, when te increase, the entrainment ratio would increase, and the system mechanical COP would also increase. In the paper, the cause of the result was analyzed using the CFD technique. The ejector entrainment ratio was affected by the operation condition and the ejector structure in the same time.