Abstract: An experiment was conducted to investigate the self-excited flow oscillation in a centrifugal fan impeller.The unsteady dynamic pressures were measured around the periphery of the impeller outlet with 8 high-response transducers.The experimental observation shows the existence of a lower frequency,nonrotating oscillation in the low flowrate conditions.The measurements also indicate that the oscillation is unstable at a short duration and at a local position,and the peripheral distribution of oscillation strength is non-uniform.The analysis shows that there may be some relationship between the self excited flow oscillation and rotating stall,especially during inception behavior of rotating stall.