The invention relates to a self-adjustable flat-flame burner for a centrifugal cast-iron pipe annealing furnace, which is characterized in that a combustion-supporting air sleeve is fixed at the bottom inside a burner nozzle with a cavity, and the side wall of the combustion-supporting air sleeve is provided with an air hole; a combustion-supporting air hose is hermetically fixed on the side wall of the burner nozzle, a main air hose is fixed on the upper end of the burner nozzle by flanges, and the lower end of the main air hose extends into the combustion-supporting air sleeve; the internal outlet of the main air hose is provided with a conical disc, and the conical disc is in threaded connection with a handle frame by an adjusting screw; the handle frame is hermetically fixed with the main air hose, and an adjusting hand-wheel 1 is fixed at the upper end of the adjusting screw; the main air hose is hermetically fixed with a bent pipe, the bent pipe is hermetically fixed with a connecting pipe by the flanges, and the connecting pipe is hermetically fixed with a blast-furnace gas conduit by a gas valve. The self-adjustable flat-flame burner of the invention has the advantages of easy clearing, adjustable flame intensity and stable burning.