Abstract: In this paper, the mechanism and dynamic process for three-dimensional evolution of the Karman vortices and the vortex filaments in the braid regions, and the structural features in the wake behind a ciccular cylinder at moderate Reynolds number (≈103) have been studied numerically. The vortex filament in the wake field are tracked by the inviscid vortex dynamics and the localized-induction approximation (LIA) method. The time-averaged velocity field of the wake and Karman vortex street flow field are consi...