Abstract: The corrosion reason for inner wall of tube of first reheater of BP-1025 boiler has been analyzed by means of macro and micro examination. The results showed that the corrosion type was oxidation corrosion caused by shutdown of units; the first reheater corrosion can be attributed to the corrosion accumulation since the units was brought into operation. The hole through the tube on the leaky tube was result of continuous corrosion on previous formed corrosion pit.