The invention relates to the field of non-transfiguration pumps for elastic fluid, in particular to a radiating fan controlled by moment of force and used for a servo motor, which comprises a front end cover (11), a rear end cover (12), a casing (2), a fan blade shaft (3) and fan blades (32). The radiating fan is characterized by further comprising a plate shaft (5), a middle plate shaft (6), a gear shaft (7), steel balls (81) and springs (83). The plate shaft (5) is sleeved in the front end cover (11) through a plate shaft bearing (51), the middle plate shaft (6) is a step shaft, a primary gear (71) is fixedly connected with the middle of the middle plate shaft (6) through a gear key (75), and the steel balls (81), steel ball piston shoes (82) and the springs (83) are all arranged in through holes of a middle plate (61). The radiating fan is simple in structure, high in protection level and wide in application range.