The invention provides a knife bending device of a numerical control knife bending machine. The knife bending device of the numerical control knife bending machine comprises a movable knife block mechanism and a fixed knife block mechanism. The movable knife block mechanism comprises a first motor, a first lead screw, a first sliding block and a movable knife block, wherein the first motor is connected with the first lead screw; the first sliding block is installed on the first lead screw; and the movable knife block is installed on the first sliding block. The fixed knife block mechanism comprises a second motor, a second lead screw, a second sliding block, a third sliding block and a fixed knife block, wherein the second motor is connected with the second lead screw; the second sliding block and the third sliding block are installed on the second lead screw; and the fixed knife block forms a V-shaped angle by hinging two stress plates, the two stress plates are hinged to one ends of two connecting rods correspondingly, and the other ends of the connecting rods are hinged to the second sliding block and the third sliding block correspondingly. By changing the structure of the knife bending device, the bending force is reduced under the condition of the same bending torque, and a thick blade can be bent by a large angle.