A cooling fan with dual blade sets has an impeller formed by a rotatable hub, a stator assembly, and a shell. A plurality of mini blades and a plurality of guide blades are respectively formed on a bottom surface and an external surface of the rotatable hub. The impeller has a plurality of holes defined on the bottom surface being arranged in a circle adjacent to the mini blades. Therefore when the impeller rotates, the mini blades are able to drive out the heat in an inner space between the impeller and the shell through the holes to outside.