At this point, "Tiny Cooling Fan" dynamic stress increases blade may cause blade breakage, so from outside the impeller absolute reference system, the stall area or rotated in the direction of rotation of the impeller, causing the mechanism of rotating stall, "Tiny Cooling Fan"rotating stall in pressure fluctuations generated by the impeller rotor excitation occurs abnormal vibration excitation force, the excitation force size and the size of the gas molecular weight, they are proportional to the relationship, the greater the molecular weight, the greater the incentive force. Rotor rotating stall frequency: When the normal operation of the cooling fan, "Tiny Cooling Fan" with the direction of the impeller rotor is in the same direction, an exception occurs when the fluid direction, the rotor is abnormal vibration. So this is the reason causing the fan rotating stall.