In this paper, a cyclic event based NOx model is developed and validated for targeting the challenges of NOx control which is primarily dependent on highly complex combustion phenomena and cyclic coupling of residual gas and energy, specially in transient mode. The model input parameters are estimated from two discrete time models with Kalman filter estimation, considering the effects of cycle-to-cycle coupling of residual gas and energy. First model is developed based on residual gas cycle-to-cycle coupling dynamics and second based on cyclic energy dynamic due to energy carrying by residual gas coupling. The in-cylinder adiabatic temperature and oxygen equilibrium concentration are then calculated using both model on cyclic event based. Finally, the cyclic transient NOx model is calibrated and validated on full scale of gasoline engine to illustrate the transient response of NOx formation.