A single-phase outer-rotor motor includes a stator and a rotor surrounding the stator. The stator includes a stator core and windings wound around the stator core. The stator core includes a yoke and a plurality of teeth. Each of the teeth forms a tooth tip at a distal end thereof. A slot opening is formed between each two adjacent tooth tips. The rotor includes a housing and a permanent magnet affixed to an inside of the housing. The permanent magnet forms a closed ring in a circumferential direction. The permanent magnet forms a plurality of magnetic poles along the circumferential direction. An outer surface of the stator and an inner surface of the permanent magnet define there between a symmetrical uneven gap. A width of the slot opening in the circumferential direction is less than or equal to five times of a minimum width of the gap.