An axial flow type cooling fan, comprising an upper casing, a lower casing, a rotor assembly, and a driving unit. The lower casing and the upper casing enclose an inner space. The rotor assembly is housed in the inner space and performs a rotational movement. The rotor assembly further comprises a plurality of blades, attached to a central shaft and having a peripheral ring, from which a peripheral rim extends outward. The driving unit has electric coils on the upper or lower casings and permanent magnets on the peripheral rim, causing the rotational movement of said rotor assembly. By the arrangement of these structural parts, an increased area of air flow and consequently increased air flow are attained, while drag and noise are reduced.