Abstract: The numerical simulations of the unsteady flow induced by rotor-stator interaction in a two-stage fan were carried out.A three-dimensional unsteady Navier-Stokes equations solver using a high-resolution finite difference has been developed.It can be used for the calculation of steady flow field with an implicit scheme.The solution of steady flow was firstly obtained by this code.The unsteady flow computations were started from this solution.The unsteady flow results show that the unsteady effects on inlet flow angles of blade rows are significant.The variations in inlet flow angles of stator blades are larger than that of rotor blades.In comparison with the steady flow solution,the increases in unsteady flow attack angle are larger than the decreases.The maximum increase is about 10 degrees.The variations in unsteady aerodynamic force on stator blades are also larger than that on rotor blades.The unsteady flow effects caused by several blade rows are different from that by single blade row.