Abstract: Based on the vertical distribution of velocities data in a radial sand ridges area of the south Yellow Sea in summer and winter, a Karman-Prandtl equation is adopted to estimate the shear velocities in seabed deep grooves. The spatial and temporal distributions of shear velocities are analysed and a new method of quickly estimating shear velocity is described. The results show that during maximum ebb and maximum flood, flow velocities follow a logarithmic distribution over the depth, with an average of 7.4 cm/s in summer, which has a decreasing tendency from north to south and from nearshore to offshore, and an average of 6.0cm/s in winter, which has a decreasing tendency from middle to north and south and from nearshore to offshore. Shear velocities in summer are greater than those in winter, and the ones in spring tide are greater than those in neap tide. The difference between shear velocities during maximum flood and ebb is small in summer and becomes large in winter. Shear velocities can be quickly estimated by using near-surface velocities in summer and winter, and it can be concluded that shear velocities roughly equal six percent of the near-surface velocities at the same locations in radial sand ridges area.