Abstract: In order to study the flow in the intake ducts and cylinder and validate numerical simulation method,steady flow test and numerical simulation for the three-dimensional flow field in combination intake system with tangent intake duct and helical intake duct had been carried out.By employing a new method brought forward to calculate the intensity of the swirl and flow coefficient from velocity field computed by compute fluid dynamic(CFD) simulation,numerical prediction had been compared with test results.Good agreement between numerical results and experimental data is demonstrated.It is found that when the airflow flows far away from valves and meanwhile the flow pattern in the cylinder gradually becomes uniform and form a vortex.It is also show that the CFD simulation could get more information on flow field and hence provide a strong basis for design of inlet duct.