In this paper, the failure analysis of finned tube bundle leakage of a flue gas heat exchanger in a high-pressure furnace was carried out. Through macroscopic examination, material chemical composition analysis, metallographic analysis, X-ray diffraction analysis of corrosion products, scanning electron microscope analysis, and energy spectrum analysis, it was found that the failure was mainly due to the inability of material chemical composition, which caused its corrosion resistance to decline. At the same time, sulfur, chlorine, and bromine in the medium caused pitting corrosion and stress corrosion cracking, eventually leading to leakage failure. At the same time, reasonable suggestions were given to avoid similar failures.