Abstract: This paper studies the simulation accuracyof automobile exterior flow field with35°Ahmed model with the commercial CFDsoftware STAR-CCM+.The research is conducted from aspects such as mesh type, turbunlance model and mesh size. We analyzedthe three levels data including the tatal pressure dragcoefficient, the local pressure drags coefficient andthe flow velocity at the selected point above the slope of the model. The evaluation of the simulation accuracy is performed step by step and stricter as it goes on. We finally worked out an acceptable and industrially applicable simulation method, which features a high-quality strategy with the main grids mostly used tetrahedral mesh, k-w turbulance model and meshsize limited to some order of magnitude. Then, we studiedy the technique of passive control drag reduction by adding the raised structure at the tail of the 35°Ahmed model.The results show that the resistance is mainly derived from the tail of the 35°Ahmed model.Adding a convex structure at the tail of the model will botainoptimal drag reduction effect when the angle between the additional plate and the inclined surface is 30°.