Abstract: The generation of sand ripple is closely related to the flow pattern, and the relation between sand ripple and flow condition is still not clear. The Particle Image Velocimetry (PIV) was used to study the flow and vortex characteristics on the ripple bed. The vortex field on ripple bed were compared with that of the flat bed. The results show that the large vortex area was concentrated on the upstream and downstream slope of the ripple while the vortex values in other areas are nearly zero. The results were helpful for the study of sand ripple generation.