Abstract: The abnormal microstructure of drill pipe weld found in the process of production inspection was analyzed by apparatuses of optical microscope, scanning electron microscope and micro Vicker hardness tester. The results show that the abnormal microstructure of drill pipe weld consisted of martensite, ferrite and troostite. It was because the tempering temperature was high and exceeded the Ac1 temperature of the joint, which resulted in partial austenitizing of the microstructure. Because the brittleness and sensitivity to erosion medium in the drilling fluid of the abnormal microstructure were rather high, it would greatly shorten the service life of the drill pipe. Strengthening the standardized operation was suggested to avoid reoccurrence of the abnormal microstructure.