Abstract: To understand the effects of centrifugal compressor inlet distortion caused by 90°bent pipe, two different axial position inlet bent pipe were numerically simulated with compressor and the influence on compressor performance was analyzed. The results show different performance deterioration between different bent pipes, the larger distance between bent pipe outlet and impeller inlet creates more decrease. The bent pipe makes the flow field of impeller inlet strongly disordered. The distortion causes a noticeable decline in compressor performance under large mass flow and a slightly drop under low mass flow. The affect of inlet distortion amplifies and develops to the volute inlet while the mass flow rate increases, which function with circumferential distortion caused by volute tongue, makes the performance decreased. When the mass flow rate is low, the inlet distortion reduces the flow loss in impeller passage, which could maintain the performance of compressor at low mass flow.