Abstract: During the drilling process of a certain well, the drill pipe joint broke. The fracture reasons of the drill pipe joint were analyzed by macroscopic observation, chemical composition analysis, scanning electron microscope analysis, mechanical property test and metallographic examination. The results show that the fracture property of the drill pipe joint was fatigue fracture. During the drilling process, frequent jumping and holding of the drill pipe resulted in a large instantaneous load, and fatigue cracks initiated at the root of the large end thread of the drill pipe. Under complex alternating loads, the cracks rapidly expanded, ultimately led to the fracture of the drill pipe joint.