The invention relates to a method and a device for extracting gas from waste classification substances by a microwave heating method so that a gas preparation process is simpler, rapider and safer, fully utilizes resources in the processing process and processes wastes into available resources to be recycled. The invention adopts the technical scheme that a microwave heating type cracking gasification furnace is adopted in a processing process of the waste classification substances; a cracking reaction chamber and a solid storage chamber in the device are integrated into a whole; raw materials enter the cracking reaction chamber to realize low-temperature cracking; gas generated by cracking is cooled, separated, stored and utilized, and carbonized solid products generated by cracking are processed into carbon coke products. The invention has the advantages that the available resources are prepared from the wastes and fully recycles the resources in the processing process so as to thoroughly process the wastes and achieve high utilization rate.