As the problem of whether the engine oil drain time recommended by vehicle manufacturer is scientific is unknown,4 civilian cars were used to take 5 groups of road tests,and every road test experienced more than 352 days.The oil samples during experimental process were tracked and collected to test the component and physicochemical properties change.The characteristics of the component and physicochemical properties of the engine oil under typical urban operating conditions were studied,and the reasonability of the recommended oil drain time was discussed based on experiments.The results show that when reaching the recommended oil change time (180 days),the total acid number and kinematic viscosity of the test mineral oil,semisynthetic oil and synthetic oil are far from the current oil drain standard.The total acid number and kinematic viscosity do not reach the oil drain standard after the experiments for 448,506,387,538 and 352 days respectively,and the experimental oils also retain good oxidation stability,detergency and dispersancy.