Abstract: In order to analyze the effect of nonsymmetrical slots on a compressor,unsteady numerical investigation on a partial circumference casing treatment and a whole circumference casing treatment with a single stage transonic axial compressor was carried out.The numerical results show that the partial one could obtain better compressor performance than the whole one,both of which contain the same number of slots.Due to the symmetry of slots,the partial casing treatment brought about large-size symmetry in the circumferential tip region,which could cause a special low-frequency unsteady effect.Moreover,it was found that the partial circumference casing treatment,which supplied both high-frequency and low-frequency unsteady effects,could improve both the tip leakage vortex and trail-edge separated vortex.