This specification discloses a serial fan comprising a plurality of rotor vanes, one or more supports and a frame. Each of the rotor vanes comprises an inlet, an outlet, and one or more blades. Each support supports at least one of the rotor vanes so that the corresponding rotor vane can rotate thereon. The frame connects all the supports. The rotor vanes are connected in series in the axial direction, and the design of each of the rotor vanes is such that the velocity vector of the air relative to one of the blades on the outlet side of the ith rotor vane plus the velocity vector of the blade of the (i+1)th rotor vane relative to that of the ith rotor vane gives the incoming velocity vector of the air relative to the (i+1)th rotor vane. This vector is essentially parallel to the extension direction of the blade on the inlet side of the (i+1)th rotor vane. Here, i is a natural number smaller than the number of the plurality of rotor vanes.