The objective of this study is to understand the generation mechanism of sound and to develop a prediction method for the unsteady flow field and the acoustic pressure field of a centrifugal fan. Lowson's method is used to predict the acoustic pressure in a free field, The scattering effect of a casing is considered by using a REM and newly developed source, A DVM(discrete vortex method) is used to model the centrifugal fan and to calculate the flow field, In order to compare the experimental data, a centrifugal fan and wedge introduced by Weidemann are used in the numerical calculation and the results are compared with the experimental data.