Abstract: The failure reasons of a platen superheater tube of a fuel-oil boiler were studied by macroscopic observation, metallographic analysis, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The result of macroscopic observation shows that creep cracking happened to the tube after working for a long time at high temperature. The result of metallographic analysis shows that the carbide precipitated at grain boundaries. The result of scanning electron microscopy(SEM) and energy dispersive spectroscopy(EDS) show that a oxidation layer formed on the inside of the tube. The thickness of the oxidation layer was 371.55 μm. It can be concluded that long-term local overheating occurred to the tube during working, leading to microstructure change and reducing the mechanical properties of the material.