Large-torque automatic fastening device

The invention discloses a large-torque automatic fastening device. The large-torque automatic fastening device comprises a power-driven hydraulic pump station (1) and a hydraulic spanner (2). The power-driven hydraulic pump station (1) is communicated with the hydraulic spanner (2) through an oil pipe (3), a pressure relay (4) is connected at the position of an oil outlet of the power-driven hydraulic pump station (1), an oil inlet of the pressure relay (4) is communicated with a high-pressure output oil path of an electro-magnetic reversing valve (1.4) in the power-driven hydraulic pump station (1), and a control port of the pressure relay (4) is electrically connected with and controls an electric magnet of the electro-magnetic reversing valve (1.4). A travel control device which can control the travel of an oil cylinder is arranged on the hydraulic spanner (2). After the structure is adopted, a bolt can be screwed in place accurately, action is fast, efficiency is high and automation can be realized.