The Realizable k-ε Reynolds averaged Navior-Stokes (RANS) turbulence models and SST k-w detached eddy simulation (DES) models are investigated for simulation of external flow and trailing vortex around Ahmed body. The 3-D N-S equations are solved with central finite volume scheme and half-implicit SIMPLE method. The time average parameters of the DES results, such as the pressure, velocity field and drag coefficient Cd, are verified by comparing with RANS and experiment data. The vortex structures of vertical, horizontal plane and cross-section, along with the turbulent kinetic energy of tail vortex are studied in details. The results show that for time averaged parameters both models can get reasonable results, while for capturing the instant flow structure, DES shows advantage over RANS model.