Abstract: By means of macroscopic examination,chemical composition analysis,microstructure examination and mechanical properties test on the material,combined with the use condition and load analysis,the piercing failure of a 127 mm S135 drill pipe were analyzed. The results show that it was the corrosion pits with stress concentration at the outer surface of drill pipe and the alternating stress,that resulted in the fatigue crack initiation and expansion quickly at the bottom of pits.