Unsteady, massive separation and complex vortex structures are the typical features of vehicle external flow field. The numerical simulation of the external flow field around a car was carried out by using DES methods. The results such as pressure distribution, skin friction coefficient distribution, velocity and turbulence kinetic energy distribution in the wake were compared with the results by using the RANS methods. It has been indicated that it has few differences between RANS and DES in obtaining the time-average results, but DES methods are particularly suited and clearly superior to RANS methods for unsteady flows and in capturing the structures which contain energy. Hence, DES methods are more suitable to calculating the complex flow field around a car. In contrast to RANS, computational cost is more expensive for DES, and RANS is economical for obtaining the time-average information of flow field.