The main source of the noise of an axial flow fan is the fluctuating pressure field on blade surfaces caused by the shedding of vortices at the trailing edge of blades.An analytical model to predict the vortex shedding noise generated at the trailing edge of blades of axial flow fans was proposed by Lee in 1993.In this model,for mathematical convenience,an idealized vortex street is considered.However,the agreement between the analytical results and the experimental data needs to be improved because of the simplification about the Karman vortex street in the wake of blade.In the present study,a modified model is proposed based on the prediction model by Lee.The boundary layer theory is used to analyze and calculate the boundary layer development on both the pressure and the suction sides of blades.Considering the effect of boundary layer separation on the location of noise source,the predicted overall sound pressure level compares favorably with the experimental data of an axial fan.In the calculation of A-weighted sound pressure level(La),considering the effect of static pressure on radiate energy,the predicted broadband noise with the modified model compares favorably with the experimental data of a multiblade centrifugal fan. The main source of the noise of an axial flow fan is the fluctuating pressure field on blade surfaces caused by the shedding of vortices at the trailing edge of blades. An analytical model to predict the vortex shedding noise generated at the trailing edge of blades of axial flow fans was proposed by Lee in 1993.In this model, for mathematical convenience, an idealized vortex street is considered. Yetever, the agreement between the analytical results and the experimental data needs to be improved because of the simplification about the Karman vortex street in the wake of blade. the present study, a modified model is proposed based on the prediction model by Lee. The boundary layer theory is used to analyze and calculate the boundary layer development on both the pressure and the suction sides of blades. effect of boundary layer separation on the location of noise source, the predicted overall sound pressure pressure level with favorably with the experimental data of an axial fan. the calculation of A-weighted sound pressure level (La), considering the effect of static pressure on radiate energy, the predicted broadband noise with the modified model comparable favorably with the experimental data of a multiblade centrifugal fan.