Numerical simulations were performed for Rotor 67 to analyze the mechanism of the stall margin(SM) improvement of circumferential grooves(CG) casing treatment

and the matching between CG and pre-swirl angle. Results showed that stall in Rotor67 was mainly attributable to the low velocity region arisen by the inference of tip leakage flow and shock wave. The mechanism of SM improvement was that the flow from the pressure side of adjacent blade caused a vortex counter-rotating to the leakage vortex(LV)

which inhibited the development of LV. The most important groove(s) changed while the distribution of static pressure changed because of the varying mass flow or pre-swirl angle. A design method was presented depending on the research results.