Abstract: Based on the analysis of structural features of the circumferential grooved casing treatment,3-D incompressible,steady,time averaged N-S equation,continuity and k-ε two equation turbulance model equations are successfully applied to the flowfield calculation in the cascade with the circumferential grooved casing treatment.The flux of the gas through the treatment groove is proposed as a new index which can quantitatively evaluate the effectiveness and the capability of extending stability by circumferential grooved casing treatment.The effects of structural parameters and treatment positions on the effectiveness of extending stability are analysed and discussed.The conclusions are proved by a great deal of testing results.The method and technique can be applied to analysis and design of the casing treatments in a compressor.