NGV engine adopts the fuel supply method of premixing natural gas and air in the premixing chamber out of cylinder, which results in the engine dynamic performances decline. It is an obstacle to popularizing and applying NGV. Using air rich in oxygen to support combustion can decrease ignition point of the fuel, enhance combustion efficiency and make much more heat available. The dynamic perfonnances and fuel consumption rate of a NGV engine with different oxygen concentration are researched in detail. The results show that the increase of oxygen concentration has remarkable influence on the dynamic performances of NGV engine. Power and Torque performances increase and fuel consumption rate decreases when oxygen concentration of premixed gas increases. The results of theory analysis and experiment research indicate that combustion-supporting using oxygen-rich air can enhance the dynamic performances of NGV engine.