Abstract: In order to prevent the occurrence of injury of belt rotating parts in the production of Tashan Coal Preparation Plant when the night shift staff is sleepy or the fog and steam in the winter plant makes the visibility low and the personnel drop coal under the belt conveyor, an infrared detecting device is designed, which is suitable for working environment of coal preparation plant and able to accurately detect human body. By detecting the size of the radius of curvature at the head (tail) position of the human body, shielding the infrared condition when the human body clears the coal falling under the belt conveyor, and corresponding length of time, the host machine can be monitored to implement on-site (or centralized control center) alarm and stop protection, so as to effectively avoid the damage of the belt conveyor to the field staff.