A fan impeller includes a hub, a shaft, a metal housing and a plurality of blades. The outer periphery of the hub has a curved surface. The shaft is disposed in the hub and connected to the hub. The metal housing has an annular shape and is disposed in the hub. A magnetic ring is disposed at the inner side of the metal housing. The blades are disposed around the outer periphery of the hub. The blades are projected along an extension direction toward the shaft to define projection areas thereof, and the projection area of a top and a bottom of any one of the blades is partially overlapped with other two adjacent blades. A distance between an outer edge of each blade and a rotational axis of the fan decreases proximate the top of the blade and then increases towards the bottom of the blade.