Abstract: This paper presents three dimensional unsteady numerical simulation of whole ring rotor/stator interaction in a single stage transonic axial compressor by using the commercial CFD software FLUENT.The different flow fields of both elongated axial gap and normal axial gap between rotor and stator are calculated and compared.The numerical results acquire clear flow pictures of rotor/stator interaction,and show the periodic oscillations and lag phenomena of outlet mass flow rate in three successive stator passages.The paper supports that the mature commercial software can be employed to study complex physical phenomena in turbomachinery.