Axial flow fan

An axial flow fan, comprising:

• a hub, configured to rotate around a center axis and having a negative pressure side and a positive pressure side opposite to each other;
• and
• a plurality of fan sets, disposed around the hub, wherein each of the fan sets comprises at least two blades, and each of the at least two blades has a wind inlet end, a wind outlet end opposite to the wind inlet end, a negative pressure surface, and a positive pressure surface opposite to the negative pressure surface in each of the fan sets, wherein a minimum distance between the wind inlet end of one of the adjacent at least two blades and the positive pressure side is greater than a minimum distance between the wind inlet end of the other one of the adjacent at least two blades and the positive pressure side, a minimum distance between the wind outlet end of one of the adjacent at least two blades and the negative pressure side is less than a minimum distance between the wind outlet end of the other one of the adjacent at least two blades and the negative pressure side, the wind outlet end of one of the adjacent at least two blades corresponds to the wind inlet end of the other one of the adjacent at least two blades, the negative pressure surface of one of the adjacent at least two blades corresponds to the positive pressure surface of the other one of the adjacent at least two blades, and a gap is provided between the negative pressure surface of one of the adjacent at least two blades and the positive pressure surface of the other one of the adjacent at least two blades.