The invention relates to a high-altitude slow descending device, which is characterized by comprising a shell, wherein the upper half part and the lower half part of the shell are respectively provided with a large-diameter rope wheel set and a small-diameter rope wheel set; a centrifugal damper is arranged between a small rope wheel axle in the small-diameter rope wheel set and the shell; the small rope wheel set is connected with the large rope wheel set through gear drive; a rope penetrates the shell from a first rope hole on the top of the shell, moves around the large rope wheel set and the small rope wheel set in the shell in turn and passes through the shell from a second rope hole at the bottom of the shell; and a braking mechanism is arranged between any one small rope wheel axleand the shell. A plurality of rope wheels are wound by the rope, so that the structure is firmer, the rope cannot slip, double functions of automatically slowly descending and manually braking are realized, and safety performance is improved; and a plurality of sets of slow descending devices can be arranged on one rope, so that the aim of slowly descending multiple persons simultaneously is fulfilled.