The failure incidents of friction crack of tool- joint box occur sometimes with the recent deep, ultra-deep wells and horizontal wells in complex working conditions, and has become an important form of failure of tool-joint box. In this paper, the macro-crack failure modes, micro-cross-section characteristics and the characteristics of phase change organizations of friction crack of tool- joint box are analyzed, and the failure mechanism of friction crack of tool-joint box is discussed by the force on the drill pipe joints, drill pipe joint materials performance , and put forward proposals and measures on how to prevent failure from the using, material properties and surface treatment of tool-joint box.