The invention relates to a flat steel bifurcated pipe and a manufacturing method thereof. The flat steel bifurcated pipe comprises a main pipe, a left branch cone and a right branch cone, wherein one end of the left branch cone is communicated with one end of the main pipe; one end of the right branch cone is communicated with one end of the main pipe; one side of the left branch cone leans against and is welded with one side of the right branch cone; another end of the left branch cone and another end of the right branch cone are respectively communicated with a left branch pipe and a right branch pipe; bottoms of the main pipe, the left branch cone, the right branch cone, the left branch pipe and the right branch pipe are located at the same one altitude. The flat steel bifurcated pipe has the advantages that the shape of the flat steel bifurcated pipe is different from the principle of the same one altitude of axial lines of various pipe joints of the other steel bifurcated pipes and ensures the same one altitude on the bottom of the various pipe joints; the same one altitude on the bottom of the pipe has independent goodness; water can flow freely to be discharged when high-pressure pipes are maintained without pumping the water by a water pump or arranging holes on the steel bifurcated pipe and connecting with a special drainage system; the drainage time is shortened greatly, and the effective work time for maintenance is prolonged; the flat steel bifurcated pipe has the advantages of regular shape, no deformity portions, reasonable force and no stress concentration phenomenon.