Abstract: Aviation kerosene requires high cleanness and no harmful substance like mechanical impurity in its usage. This paper discusses the case of using hydrocyclone in the two-phase separation of kerosene and impurity. Numerical simulation is used to simulate the separation process of kerosene and impurity in the liquid-solid hydrocyclone and the impact of impurity diameter and inlet throughput on separation efficiency. The calculation result shows that the re-pollution of kerosene by the separated impurity and loss of kerosene can be avoided if the valve at the downflow pipe of hydrocyclone opens and closes at proper time. The impurity can only be effectively separated when its diameter is above a certain value and there exists a better range in the throughput of hydrocyclone. These results can provide guidance for the operation of hydrocyclone in practical application.