A modal experimental study has been carried out on a new water and sediment separation device-circular rings desilting and sediment ejection basin. In this study it has been tested the velocity distribution of eight redial test sections respectively in radial, vertical and circular direction. The results indicate that the distribution of velocity and velocity gradient in the ring direction of circular rings is uneven and the largest numerical value emerges in 180° radial test section. Additionally, velocity and velocity gradient are inversely proportional to the radius in the radial direction, and surface water velocity is inversely proportional to water depth in the vertical direction. Besides, flow turbulence in the distance less than 1/2 radius is strong, while in other distance is weak. Furthermore, velocity in the central outflow ring reaches the maximum value of 7.3 times that of overflow weir inside, and the overflow weir length is 15 times that of central outflow ring. Overall, the experiment shows that the circular rings have better desilting conditions for the long overflow weir length.