A numerical investigation was carried out on the transonic axial-flow compressor Rotor 67 to clarify the stall mechanism and the influence of self recirculation casing treatment(with three injection positions) on its performance. The result showed that low-speed region in the tip leakage vortex played a major role in stall. Casing treatments with three different injection positions improved the aerodynamic stability of compressor

and those with forward injector gives less improvement (2.72%) on stall margin than those with center (13.43%) and backward (9.47%) injectors. Casing treatment with center or backward injector performed better in suppressing the tip leakage flow

thus reducing the spreading of low energy fluid. Additionally

the backward injector showed no effect in accelerating the blockage around pressure side leading edge and suppressing the low energy leakage

so the ability of improving flow-filed of backward injector was lower than that of center injector.