A numerical investigation for a centrifugal blower is implemented to study the swirling flow influenced by distorted flow at volute's inlet. The distorted inflow is given out by computation, when the mathematical model involves the whole machinery. Three different vortices including inlet vortex and a pair of trapezoid vortices are captured in several prescribed radial cross sections of volute. Each vortex experiences its own developing process, which contributes to explain the loss variation in volute. As compared with the swirling flow calculated according to a uniform inflow of volute, the swirling flow influenced by a distorted inflow of volute is quite different from that, which concludes that more appropriate numerically results can be obtained in consideration of the distorted inflow of volute.