The invention relates to a square steel wire bending mechanism capable of tightly jacking a steel wire. The square steel wire bending mechanism comprises a rack and a power distribution control box, asteel wire conveying device, a steel wire clamping device and a steel wire bending device which cooperate with each other and are matched with the steel wire are arranged on the rack, the steel wireclamping device comprises a clamping groove arranged on the rack and matched with the steel wire, a steel wire tightly-jacking device matched with the steel wire passing the clamping groove is arranged on the side face of the clamping groove and comprises a clamping shaft arranged on the rack, a clamping convex block is arranged on the clamping shaft, a clamping connection rod is hinged on the clamping convex block, a clamping top block matched with the steel wire is arranged on the upper portion of the clamping connection rod, and a clamping cooperation gear is socketed at one end of the clamping shaft and connected with a driving motor through a clamping transmission gear. The steel wire clamping device realizes clamping through cooperation of the clamping groove and the steel wire tightly-jacking device, so that downward bending of the steel wire due to downward bending force during bending is avoided, and the bending device is ensured to only act on a portion to be bent.