Abstract: An adjustable crank for adjusting the swinging-angle of a fan comprises a first and a second eccentric disks, the first disk is rotatablely inserted in the second disk, a ring-shape spring is disposed between the engaging surfaces of them to couple them with predetermined torque. A crank pin is eccentrically and integrally formed on the first disk. The second disk is provided with a rotation means for the second disk being turned to rotate about a center axis, which is eccentric with respect to the engaging surfaces. A rotary knob is fixedly mounted on the end of the crankpin for manually turning the first disk to rotate relative to the second disk. Thereby the crank length can be continuously adjusted and self-fixed after being adjusted. Apparently, it is unusually simple in structure, very easy to adjust, especially convenient and cheap in manufacture, and reliable in running.