Abstract: Numerical prediction of fan noise is very difficult work because of the restriction of the computer technology. The main noise source in a centrifugal impeller is the fluctuating force on blade surfaces caused by the vortex shedding from blade trailing edges. So a method of numerical prediction of vortex shedding noise radiated by a commercial centrifugal impeller is presented, based on a vortex flow model developed by Lee in 1993. Three main research works are included in the method. First, in order to predict the aerodynamic performance a numerical simulation of 3-D turbulent flow field of the impeller is completed using commercial CFD software Fluent and well validated by the experiment. Then, the velocity profile near the wall at the trailing edge of the blade is analyzed in detail to determine the boundary layer thickness both on the pressure and suction sides. Finally, the total SPL of the noise is predicted and the results agree with the experimental data within 3 dB near the design operation.