A cross-flow fan comprising the following features wherein the words top, bottom and lateral refer to a position of the fan in which its axial direction, which is the direction of its rotation axis, is vertical: a fan frame having a first cover portion, a second cover portion and a lateral wall portion arranged between the first and second cover portions (11 and 12), wherein the lateral wall portion has an air inlet and an air outlet; a driving module as a stator of a motor received in the fan frame and coupled with the first cover portion; and an impeller (3, 4, 5) as a rotor of the motor having a hub and a plurality of vanes, wherein the hub is rotatably coupled with the driving module, and the vanes are coupled with the hub; wherein the hub has an air-guiding protrusion facing the second cover portion and each of the vanes has a top edge facing the second cover portion, the air-guiding protrusion has a top point being an outmost point(s) of the hub most adjacent to the second cover portion, and the top edge of each of the vanes is higher than the top point of the hub in a axial direction of the hub, wherein a bottom part of an outer periphery of the hub has the same axial position in the axial direction of the hub as a bottom part of the rotor of the motor, wherein the hub forms an elevated part from the top point to the outer periphery thereof, and wherein the elevated part of the hub receives the driving module, wherein the cross-flow fan is characterized in that the top point is a single top point, the air-guiding protrusion of the hub is a cambered face having a centre at which the single top point is located, and the single top point is located on the rotation axis of the cross-flow fan. a fan frame having a first cover portion, a second cover portion and a lateral wall portion arranged between the first and second cover portions (11 and 12), wherein the lateral wall portion has an air inlet and an air outlet; a driving module as a stator of a motor received in the fan frame and coupled with the first cover portion; and an impeller (3, 4, 5) as a rotor of the motor having a hub and a plurality of vanes, wherein the hub is rotatably coupled with the driving module, and the vanes are coupled with the hub; wherein the hub has an air-guiding protrusion facing the second cover portion and each of the vanes has a top edge facing the second cover portion, the air-guiding protrusion has a top point being an outmost point(s) of the hub most adjacent to the second cover portion, and the top edge of each of the vanes is higher than the top point of the hub in a axial direction of the hub, wherein a bottom part of an outer periphery of the hub has the same axial position in the axial direction of the hub as a bottom part of the rotor of the motor, wherein the hub forms an elevated part from the top point to the outer periphery thereof, and wherein the elevated part of the hub receives the driving module, wherein the cross-flow fan is characterized in that the top point is a single top point, the air-guiding protrusion of the hub is a cambered face having a centre at which the single top point is located, and the single top point is located on the rotation axis of the cross-flow fan.