A centrifugal fan includes a frame and an impeller. The impeller is disposed within the frame. The impeller includes a hub, a first blade group and a second blade group. The hub includes a center part, an inclined part and a connection part. The first blade group is connected with the connection part of the hub. The second blade group is disposed on the inclined part of the hub. There is a first distance between the second blade group and the first blade group. There is a second distance between the second blade group and the center part of the hub.