In this paper, due to its advantages of high accuracy and moderate computational cost, detached eddy simulation (DES) is adopted to observe detail flow characteristics of a kind of vertical axial wind turbine equipped with four helical blades. The numerical results obtained from the method have been validated by experiments as well as been compared with those from unsteady Reynolds-averaged Navier–Stokes equations (U-RANS). Several critical parameters, such as the torque, power coefficient, and tangential force, are studied in detail. It is found that the results from DES are closer to the measurement data than those from U-RANS. And, the characteristics of the flow field in the turbine can be clearly revealed by DES. Furthermore, the effects of tip vortex, Reynolds number, and pitch angle on turbine performance have also been analyzed and discussed.