Abstract: In order to analyze the directivity performance of tone noise of propeller operating in a nonuniform flow,a numerical model,based on Ffowcs William-Hawkings equation,for predicting far-field propeller noise due to non-uniform flows is proposed which requires the aerodynamic sources to be integrated over the actual blade surface.The influence of blade number,inflow harmonic and unsteady blade forces on the directivity of radiated t one noise are discussed,which shows that the characteristics coupling factor between inflow harmonic and the rotating blades play important roles in the directivity feature.When the characteristic coupling factor equal s to zero,the total radiated noise is mainly created by the axial force and the main inflow harmonic,while for the characteristic coupling factor not equals to zero,however,the noise contribution due to the axial force and the main inflow harmonic only dominate near the propeller axis,while the tangential force and the inflow harmonic that equals to the blade number dominate in the direction vertical to the propeller axis.