In this paper, using Nissan car engine oil as the research object, their main physical and chemical performances and three factors of oil carrying capacity such as the maximum non-seizure load PB, sintering load PD and the composite wear value ZMZ are experimental analyzed in different mileage. And decay law of the lubrication performances are discussed. It was found that, after used a certain time, the oils film strength reduced relatively fast, the limit ability to work reduced not obvious, and its anti-extrusion capability will gradually deteriorate with the increase in the running time.