A numerical simulation is presented to investigate the flow field inside a centrifugal blower.The numerical simulation is performed with the simultaneous calculations of the flow fields in both the whole impeller passages and the volute by "Frozen Rotor Approach".The distorted inlet flow of the volute resulted from the asymmetrical volute construction is captured and as a result,many special flow details inside the blower are obtained,which concludes that the interaction between the impeller and volute induced by the volute's asymmetry can result in many asymmetrical characteristics of the flow field.The study helps to reveal the flow characteristics inside a centrifugal blower,and to contribute to its optimized design.