Abstract: Abstract: Because of high pumping loss under part loads and the low compression ratio, gasoline engines have very poor fuel economy. Therefore, in order to reduce the fuel consumption of gasoline engines, this paper mainly studied the influence of EGR coupling with different excess air coefficients on the combustion characteristics, fuel economy, and emission characteristics under part loads of the gasoline engine. The engine used in this experiment was a 1.5L 4-cylinder gasoline engine, with port fuel injection and turbocharged, which had a peak power of 110 kW @ 5600r/min. Before the experiment, the inlet and exhaust systems of the engine were modified, and equipped with a water-cooled EGR system. The EGR gas flowed out after the three-way catalytic converter, then entered an EGR cooler, and mixed with the fresh air in the intake pipe before entering the compressor, and at last entered into the cylinders. And this EGR system was also called a low pressure loop system. During the experiment, the engine operated at a part load point, 2000 rpm and 0.5 MPa BMEP. The EGR ratio and excess air coefficient were changed to study the effect on the combustion characteristics, fuel economy, and emission characteristics under the part load of the gasoline engine. The results showed that with the increase of the EGR rate and excess air coefficient, the rate of cycle-to-cycle variation of the combustion increased, the combustion duration became longer, and that the EGR was the main factor affecting both of them. The brake specific fuel consumption decreased significantly, because of the dramatic reduction of the pumping loss. Comparied to the condition of EGR ratio=0 and α=1, the brake specific fuel consumption decreased by 8.37% under the condition of EGR ratio=20% and α=1.1. With the increase of the EGR rate and excess air coefficient, THC emission increased, but NOX emission decreased significantly by about 80%. Therefore, combining the three-way catalytic converter with EGR technology can greatly improve the fuel economy of the part load of the gasoline engine, and may meet the emission regulation of Euro 5 at the same time.