A pyrolysis-combustion dual-bed system comprises a fluidized bed, a cyclone separator, a coal ash distributor, an ash-coal mixer, a lower pyrolysis bed, a return feeder and a cleaner, wherein the cyclone separator is connected with an upper lateral side of the fluidized bed, the outlet end of the cyclone separator is connected with the inlet end of the coal ash distributor; the two outlets of the lower pyrolysis bed are respectively connected with the inlet of an external bed and the inlet of the cleaner; the outlet of the external bed is connected with the inlet of the return feeder; the return feeder close to the lower lateral side of the fluidized bed is connected with the inlet on the lower lateral side of the fluidized bed; and the outlet of the cleaner is connected with the inlet of the lower lateral side of the fluidized bed.