Abstract: Because of its simple operation,low operation cost and small physical size,cyclone is widely used in chemi- cal separation industry. The internal flow field plays a key role in its separation accuracy and efficiency. It is important to simulate the flow field accurately. The internal flow field of cyclone has a high gradient and strong swirl characteris- tics,especially the presence of central air core,which increases the uncertainty of its numerical simulation. Using the CFD software,a gas-fluid unsteady numerical simulation was carried out systematically for a 75 mm classic cyclone. The effect of different turbulence models,pressure-velocity coupling methods and discrete schemes on the calculation results of flow field were studied. Also,the diameter of the air core,tangential and axial velocity were compared to find more suitable numerical solution methods for calculating the flow fields of cyclone. The results show that RSM can ac- curately predict the flow field of cyclone,except the velocity near the air core which is lower than the experimental da- ta. The flow fields predicted by RNG k-epsilon,Realizable k-epsilon and Standard k-epsilon turbulence models are quite different from the actual flow field. And the error of RNG k-epsilon model is slightly lower than that of Realizable k-epsilon and Standard k-epsilon turbulence models. There is little difference between QUICK and Second Order Up- wind discrete schemes in predicting the internal flow field of cyclone. The Third-order MUSCL,Power Law,and First Order Upwind discrete formats could not obtain the complete air core in the flow field. The pressure-velocity coupling methods,including PISO,Coupled and SIMPLE algorithm have little effect on the calculation results. The SIMPLE al- gorithm is more suitable to predict the flow field of cyclone. Compared with PISO,SIMPLE algorithm,the diameter of air core predicted by the Coupled algorithm is larger and velocity is smaller in the overflow section. In the partial cone, the diameter of air core is smaller,but velocity is higher.