Abstract: In order to extend the stall margin of a centrifugal compressor with splitter blade,two different circumferential groove casing treatments were designed in this paper.The flow fields in compressor with smooth wall and with treated casing were numerically simulated.The results show that the first circumferential groove treated casing extends the stall margin of the centrifugal compressor by 10%,and it also has little influence on pressure ratio and efficiency.The main reason of extended stall margin was that about 75% axial chord of the tip flow field has been improved.The second scheme did not extend the stall margin,because the position of circumferential groove was not accurate,and the groove was too deep.