The invention relates to a drill pipe quick-connecting mechanism comprising an upper joint, a lower joint, and an O-shaped ring. The O-shaped ring is installed in an upper joint sealing slot and used for sealing the upper joint and the lower joint. The upper joint and an upper drill pipe are in threaded connection, and the lower joint and a lower drill pipe are in threaded connection. The upper joint thread of the upper joint can be of two different apertures and can be connected with drill pipes of two different apertures, and therefore, quick connection with drill pipes of two specifications is realized. When the upper joint and the lower joint are connected, the side of an upper joint stopper and the side of a lower joint stopper contact each other. When rotating, the upper joint transfers torque to the lower joint through contact of the two sides. An upper joint axial block piece contacts the end face of the lower joint stopper, and bears the axial tension during drill pipe lifting. The mechanism of the invention has the characteristics of compact structure, good sealing performance, large stress area, long service life, convenient disassembly, and the like. The problem that a drill pipe is complex and cumbersome in disassembly and is easy to deform and damage previously is well solved.