A simple and convenient method is presented for main dipole source identification in a centrifugal fan. By this method, the time derivation of the static pressure fluctuation on solid wall is treated as the identification parameter, and its root mean square value is defined as surface dipole strength. The main dipoles are located at the zones where the dipole strengths are much higher. Since this method is just on the basis of the three-dimensional numerical simulation of the completed unsteady flow field in the fan, the fussy numerical prediction of sound field is avoided. Although the method cannot provide a quantitative prediction on the noise or the noise reduction, the applications of this method could contribute significantly in revealing the sound generation mechanisms inside centrifugal fans and be valuable for noise reduction of centrifugal fans. By applying to guidance the noise reduction of the T9-19No.4A centrifugal fan, the dipole source identification method is verified to be feasible.