Abstract: The fracture reason of 42MnMo7 drill pipe was analyzed by means of chemical compositions analysis, fracture analysis, metallographic examination and scanning electron microscopy(SEM) observation. The results showed that drill pipes were effected by the alternate stress, making the cracks initiated on the bottom of thread stress concentrated, meanwhile the martensite layer in the pipe body reduced the toughness and plasticity, which made the crack propagate, and eventually the drill pipe was fractured. And the corresponding solutions and suggestions were proposed.