A simplified model of the intake and exhaust gas flow system for an in-line four cylinder HCCI engine with the exhaust rebreathing system was constructed. The model predicted the mass of EGR and its accuracy was verified by comparing with various experimental results. In addition, ignition timing was calculated by using the predicted mass of EGR. The results show a good agreement with experimental results and the availability of the model in ECU is indicated for its fast calculation time.