A thin fan includes a frame and a driving device. The fan frame includes a base and a frame shell. The driving device includes a stator structure and a rotor structure disposed corresponding to the stator structure. The stator structure includes a stator pole group, a bushing, a bearing and a compression-resistant pillar. The rotor structure includes a hollow-cylindrical shaft, a rotor shell, a magnetic structure and an impeller. The shaft is mounted on the outer periphery of the compression-resistant pillar and is disposed between the compression-resistant pillar and the bearing. The rotor shell is connected to the shaft. The magnetic structure is disposed on the inner wall of the rotor shell, and the impeller is connected to the rotor shell. The maximum height of the rotor structure is lower than the height of the compression-resistant pillar when the rotor structure is connected to the stator structure.