Abstract: Compared with conventional towing tank,Circulating Water Channel(CWC) has many advantages.It is being widely used in developing ship hull form and on research of hydrodynamic performance of ships.The CWC adopts separators to simulate multi-layer flow in the oceanic environment.However,they may destroy the flow uniformity at the test section in some degree because of the retardation.The CWC in the cases of no separator,integrated separator and piecewise separator were simulated and results show piecewise separator is optimal.On the other hand,high standards of horizontality are required as a basic laboratory facilities.But the inclination caused by installation error and uneven sedimentation would ruin the high quality of the flow field at the test section.CWCs at large angles were simulated and the results show that wave patterns changes a lot and air bubb les will ruin the experiments.However,changes are not significant at very small angles of inclination.The present numerical results provide some recommendations to the design of CWC.