The influences of axial skewed slot casing treatment on the performance of a transonic single stage axial-flow compressor were investigated through three-dimensional(3-D) numerical method. The numerical results indicate that the stable operating range of axial compressors is enlarged and the compressor efficiency is increased with casing treatment appreciably. The flow mechanisms of affecting compressor performance were obtained by analyzing in detail the flow-filed in compressor rotor with casing treatment. It was found that the starting location of flow separation near rotor blade suction was moved backward by the back flow formed in the slots

which weakened the adverse influence rooted in interaction of separated flow and tip leakage flow and improved the current ability of blade tip passage. So the compressor stall was suspended.