The invention relates to a steel bar binding machine, which comprises a shell, a trip gear and a multi-link band wire mechanism, a wire binding mechanism and a wire clamping and breaking mechanism arranged inside the shell, wherein the trip gear is hinged on the shell, and the multi-link band wire mechanism comprises transmission gears I and II, a transmission connecting rod and a multi-link mechanism, and a transmission gear III is engaged with a gear arm of the trip gear; the wire clamping and breaking mechanism comprises a wire clamping and breaking motor, a wire clamping and breaking shaftand wire breaking blades, wherein one end of the wire clamping and breaking shaft is connected with the wire clamping and breaking motor, the other end of the wire clamping and breaking shaft is connected with wire clamping and breaking gears III and IV, and the wire clamping and breaking gears III and IV are connected with the wire breaking blades I and II; and the wire binding mechanism comprises a wire binding motor, a wire binding shaft and a wire binding head, wherein the wire binding motor is connected with the wire clamping and breaking shaft through the wire binding shaft, and the wire binding head is rotatably connected with the wire breaking blade I. The steel bar binding machine has the advantages of reasonable design, small volume, simple structure, low manufacture cost, simple operation, high reliability, and convenience for building operations.