The characteristics of combustion and emission on the engine with oxygen-enriched intake air (oxygen concentration 21%-27%) in the idling condition after the start were investigated to understand the feasibility of improving the performance of engine. The oxygen-enriched air offers improving combustion, promoting the stability and reducing CO and HC obviously. In fact the low enrichment make NOx emission keep the smaller decreasing amplitude in the idling condition. It is recognized that the oxygen enrichment in the idling can bring a potential to control combustion and emission. This experiment results show that the function of oxygen-enriched intake air is more important for the HC and CO in the lower degree of oxygen enrichment, such as 23%~25%, and the weaker as the oxygen enrichment arrives in a higher level. Reversely the more enrichment leads to a serious consequence of NOx. Therefore it is important to balance a comprehensive profit for HC, CO and NOx emissions. Through detecting variation of instantaneous velocity, it is indicated that as the oxygen enrichment increases the peak pressure goes up, the position angle of peak pressure also keeps in advance, and the cycle variation decreases.