Auto driving and safe driving constitute a control system which has multiple variables and features of uncertainers and delay response. Anautomobile and its suroundings are considered as a whole and an auto-suroundings feature model is presented based on knowledge expressing method which describles the status appear in the driving process. The constitution of auto driving auxiliary operation expert system is discussed. The computer simulation results show that the proposed knowledge expressing method and sysytem constitution method are effective and feasible .