Abstract: The superstructures of ships can generate different scales of vortices, a threat to the helicopter maneuvering. Aiming at the problem, the characteristics of the ship airwake is investigated in this paper with CFD method instead of the traditional Reynold-Averaged Navier-Stokes(RANS) method. In particular, Detached Eddy Simulation(DES) method is adopted to investigate the transitional flow field. Through processing the transitional data, a mean flow field is obtained, which agrees well with the experimental results, validating the effectiveness and accuracy of DES over RANS in solving ship airwake. Furthermore, by observing the transitional vortices, flow separation, and reattach of ship airwake with DES method, it is concluded that vortexes' asymmetry is the main feature in wake flow, and the vortical magnitude sharply increases at the chimney, inducing a severe threat to the helicopter.