Abstract: An experimental study on increasing the mixing uniformity in the intake manifold and improving the fuel economy was carried out on a China Ⅵ natural gas（NG） engine. Firstly,a structure optimization of the intake system,including the installation of a spoiler,on the mixing uniformity was analyzed. Then,an influence of the high and low pressure exhaust gas recirculation（EGR） system on engine combustion and performance was studied. Finally,the potential of achieving high efficient combustion was explored. The results show that the structure optimization of the intake system can significantly improve the uniformity of the mixture,leading to a reduction of the cylinder-to-cylinder combustion variation and an improvement of the engine fuel economy. The application of high and low pressure EGR system can easily introduce a desired EGR amount by not relying heavily on a high preturbine exhaust pressure,which allows to use a larger turbocharger. As a result,the pumping loss is significantly reduced. Meanwhile,the high and low pressure EGR system decreases the intake manifold temperature and extends the mixing time for a better mixing uniformity. Experiment results show that more efficient combustion and lower pumping losses make the brake thermal efficiency（BTE）of the engine to increase from 39.12% in baseline to 40.63%,an improvement of 3.9%.