The invention discloses a micron-grade dry mist dust suppression device for a belt conveyor. The micron-grade dry mist dust suppression device comprises a micron-grade dry mist machine, a water-gas distributor and a dry mist box assembly. A water pumping pipe and an air compressor are arranged to supply water and air to the micron-grade dry mist machine. The micron-grade dry mist machine sets the air pressure, the air flow, the water pressure and the water flow after filtering supplied air and water and controls to open and close a valve, and the air and water are conveyed to the water-gas distributor through pipelines. The dry mist box assembly comprises a sealing cover and a plurality of universal spray nozzles arranged inside the sealing cover. The sealing cover is arranged at a powder transfer point of a conveying path of the belt conveyor. The water-gas distributor is connected with all the universal spray nozzles through pipelines and lines and controls sprayed mist and diversion of all the universal spray nozzles through a programmable logic controller (PLC) according to the operation condition. The diameter of mist particles sprayed by the micron-grade dry mist dust suppression device is 1-10 micrometers, raise dust generated in the conveying process of coal ash of coal fields can be well treated, the site environment cleanliness is guaranteed, and the physical health of on-site workers is guaranteed.