Abstract: A three-dimensional RNG turbulent model and VOF method were applied to simulation of the water-air two-phase flow field in a circular rings basin of desilting and sediment ejection, a new type of secondary sediment-treatment facilities. The calculated distributions of average velocity are in good agreement with experimental data. The results indicate that physical model tests can be replaced to some extent by numerical simulation effectively to improve research efficiency, and the latter can be used to overcome insufficient measurement of flow velocity on physical models. In the circular rings regions of this basin, the radial component of water surface velocity is numerically greater than its axial and tangential components, sharply decreasing radially and vertically, and in circle ring a recirculation zone appears along radial direction.