In order to study the flow field characteristics of a boundary layer on non-smooth car body surface, large eddy simulation and realizable turbulence model were used for the numerical simulation and calculation of external car body flow field in both transient-state and steady-state. Then, the flow field parameters, such as velocity, thickness of viscous sub-layer, wall shear stress, surface friction coefficient, turbulence intensity and turbulence dissipation rate within the boundary layer of both non-smooth and smooth model, were compared and analyzed. The influence of the non-smooth surface upon the flow field characteristics of the car body was analyzed. The results show that the velocity within the boundary layer of the non-smooth model is obviously higher than that of the smooth model, and boundary layer thickness, wall shear stress, local frictional resistance coefficient, turbulence intensity and turbulence dissipation rate are also less than the smooth model. The introduction of non-smooth surface contributes to the mixing effect of the wake flow of the carbody, preventing the ejector effect upon outside high-speed flow to internal low-speed flow, thus reducing the loss of energy of the car body flow field.