The paper reports the studies on how the three-way catalytic converters behave under full load condition of a 1.7L turbocharged engine with the mixed CNG and Gasoline fuels. The main focus of the work is the pollution reduction of the three-way catalyst. Results show that the amount of pollution is dependent on how much percent CNG is mixed in the exhaust. A numerical model was investigated with the Fire software to characterize the amount of the exhaust pollutants HC, Co and NOx. Achieving a minimum percentage of pollutant in front of the matrix surface of the catalytic converter is an important target in the development of an engine, due to thermodynamic, chemical and cost requirements. The flow distribution influences the catalyst’s conversion rate, as well as its resistance to ageing and the necessary precious metal loading. The main objective of this simulation is to help us understand how the catalyst works. The simulation interprets some of the phenomena observed in the experiments, also to shed lights on the mechanisms of catalytic actions. The simulation results the behavior of HC, CO and NOx at the output of catalyst.