The numerical flow analysis in a multistage centrifugal compressor is presented.More importance is attached to the aerodynamic performance of the stationary components inside the compressor,such as deswirl cascade and two types of crossovers.The vortex structure inside the deswirl cascade is also studied to disclose its influence on the aerodynamic performance.Jameson central scheme with BaldwinLomax turbulence enclosure is applied to Reynold's timeaveraged NS equations.The numerical investigation indicates: the flow through those stationary components may be distorted,resulting in the deviation of operating condition for the downstream rotating impeller and in decrease of the total aerodynamic performance of the whole machine.The design of rotating impeller of multistage centrifugal compressor should fully take into account the upstream flow distortion.