A fan of a vacuum cleaner includes a motor, an impeller, and a diffuser. The diffuser includes a bottom plate and guide vanes disposed on the bottom plate. The guide vanes are evenly spaced and arranged along a circumferential direction of the bottom plate. Each guide vane extends obliquely from an inner edge to an outer edge of the bottom plate. An outer end of each guide vane extends beyond the outer edge of the bottom plate. Each guide vane is deflected an angle of 30 to 70 degrees with respect to a tangential direction of the bottom plate at the inner end of the guide vane. The outer end of each guide vane is deflected an angle of 35 to 120 degrees along a circumferential direction with respect to the inner end of the guide vane.