In the present study, the effects of bell mouth geometries on the flow rate of centrifugal blowers were numerically simulated using a commercial computational fluid dynamics (CFD) program, FLUENT. A total of 12 numerical models were prepared by combining the different values of bell mouth radii and gaps between the bell mouth and the upper fan case; the cross section of bell mouth was chosen as a circular arc. All models were meshed with hexahedra elements using the Gambit software. The frozen rotor method combined with a realizable k-epsilon turbulence model and nonequilibrium wall function was used to simulate the three-dimensional flow inside the centrifugal blowers. CFD investigation showed that the bell mouth radius had a strong effect on the flow rate, which can vary by more than 5% with different bell mouth models, whereas the effect of the gap between the bell mouth and the upper fan case on the flow rate was weaker. On the basis of CFD results, experiments were carried out for five typical bell mouths to verify the effect of the bell mouth radius, the gap between the bell mouth and the upper fan case on the flow rate. CFD results were validated by the good agreement between the CFD results and the parallel experimental results.