The invention discloses an on-line air-hanging insulator lifting device which comprises a frame and a pulley block, wherein a reducing motor is arranged on the frame; a steel wire rope roller is connected with an output shaft of the reducing motor in a sleeving manner; a steel wire rope is wound on the steel wire rope roller; one end of the steel wire rope is fixed on the steel wire rope roller; the connecting end of the steel wire rope which winds around the pulley block penetrates through a top plate of the frame and is positioned inside the frame. The rotating torque is provided by using the reducing motor, and the position of an air-hanging insulator is ascended or descended through the steel wire rope or the pulley block consisting of three fixed pulleys. The online air-hanging insulator lifting device is simple in structure, convenient to use and high in degree of automation. A sampling insulator is usually positioned outside a case of an on-line salt deposit density detection device, and when measurement is required to be performed, the sampling insulator is lifted to the interior of the case of the on-line salt deposit density detection device through a lifting mechanism.