The aeroacoustic characteristics and noise reduction method of a centrifugal fan for a bagless vacuum cleaner were studied. The major noise source of vacuum cleaner is the centrifugal fan. The impeller of the fan rotates over 30000 rpm and generates very high-level piercing noise. It was found that the dominant noise source of the fan is generated from the aerodynamic interaction between the highly rotating impeller and stationary diffuser. In order to reduce the high tonal sound generated from the aerodynamic interaction between the impeller and diffuser, tapered impeller was carefully designed and tested. The trailing edge of the tapered impeller was inclined and this reduces the flow interactions between the rotating impeller and the stationary diffuser because of some phase shift. The static efficiency of the new impeller is slightly lower than the conventional one. The overall SPL is reduced about 3.6 dBA. The SPL of blade passing frequency(BPF) is reduced about 6 dBA and the $2^{nd}$ BPF is reduced about 20 dBA. The vacuum cleaner with the tapered impeller has lower noise level than that of the previous impeller and the strong tonal sound was dramatically reduced.