The invention discloses a steel bar automatic positioning device. A base is fixed into a thread roller, a jacking rod guiding seat is mounted on the base, and a positioning component slides in the jacking rod guiding seat. A lead screw is arranged on the right side of the positioning component and sleeved with a nut, the nut is fixed into a transmission seat, and a bearing is mounted on the rightside of the transmission seat. A guiding sleeve is mounted in the bearing and connected with the lead screw, a guiding key is mounted on the guiding sleeve, and the guiding sleeve transmits torque tothe lead screw through the guiding key. A large belt wheel is mounted on the guiding sleeve and connected with a small belt wheel through a synchronous belt, the small belt wheel is connected with a motor, and a zero-position detecting block is mounted at the rightmost end of the lead screw. An in-place detecting switch support is mounted on the transmission seat, an in-place detecting switch is fixed to the in-place detecting switch support, and a zero-position detecting switch is fixed to the transmission seat and located on the right side of the zero-position detecting block. The steel barautomatic positioning device has the beneficial effects that positioning automation of steel bars in equipment is achieved, and the steel bar machining production efficiency is improved.