The utility model relates to a steel bar pre-bending device. The device comprises a hydraulic clamp which comprises a movable handle and a fixed handle, wherein the front end of the fixed handle is connected with a longitudinal stretching shaft; the movable handle is used for controlling the stretching shaft to stretch; a steel bar clamping groove is formed in the front end of the stretching shaft; two supporting arms as long as each other are arranged on two sides of the fixed handle of the hydraulic clamp; one end of each of the two supporting arms on the same side of the fixed handle of the hydraulic clamp is connected with the fixed handle of the hydraulic clamp by means of welding, and the other end extends to the upper and lower sides of the steel bar clamping groove respectively; a steel plate is welded at the end part of each supporting arm; the steel plates have bolt holes; the two bolt holes in the two supporting arms on the same side of the fixed handle of the hydraulic clamp are opposite to each other, and one bolt is inserted into the two bolt holes.