Abstract: To investigate flow in a single-stage axial flow compressor with splitter rotor,numerical simulations were carried out by using a 3-D CFD code.The results show strong unsteady flow phenomena in the rotor passage,although the isentropic efficiency shows small change with respect to time.The analysis shows that differences of mass flow and pressure rise between the two splitter-splitted passages have significant influence on unsteady flow in the compressor stage.The presence of splitter reconstructs the balance of pressure in rotor passage,and controls the flow near rotor blade.