The invention discloses an automatic reversing mechanism for a plug tapping machine. The automatic reversing mechanism is characterized by comprising an output shaft, an input shaft, an intermediate shaft and an air cylinder, wherein an input shaft gear is arranged on the input shaft; an intermediate shaft gear I and an intermediate shaft gear II are arranged on the intermediate shaft; an output shaft gear is arranged on the output shaft; the input shaft is connected with the intermediate shaft gear I in a meshed manner through the input shaft gear; the intermediate shaft is connected with the output shaft gear through the intermediate shaft gear II; a reversing male spline is arranged between the output shaft and the output shaft gear; a moving fork rod, a moving fork plate and a connecting component are arranged at the bottom of the air cylinder; the moving fork rod is connected with the moving fork plate; the moving fork plate is connected with the connecting component; and the connecting component is connected with the reversing male spline. According to the automatic reversing mechanism, the automatic reverse of the plug tapping machine is achieved, a motor is prevented from being frequently started and stopped during the processing process of traditional plugs, and the energy consumption is reduced.