The invention discloses a rear pass mechanism for a cold upsetting forming machine, comprising a positioning screw, a compressed rod, and a positioning guide sleeve in a rear pass hole of the machine body, the positioning screw and the rear pass hole of the machine body are in a threaded connection, the positioning guide sleeve is fixedly disposed in the rear pass hole of the machine body, the compressed rod is movably disposed between the screw and the positioning guide sleeve, the positioning screw is a hollow screw, and a rear pass push rod pushed by a rear pass rocker arm is moveably inserted into the positioning screw, the rear pass mechanism is characterized in that: the rear pass mechanism for the cold upsetting forming machine is provided with an electric adjusting device and a thread locking device. The rear pass mechanism in the invention is advantaged by capability of realizing automatic adjustment and automatic locking of the positioning screw, and automatically detecting distance adjusted by the positioning screw, convenient and reliable adjustment, and high efficiency.